I'm working on modernizing Rosetta Code's infrastructure. Starting with communications. Please accept this time-limited open invite to RC's Slack.. --Michael Mol (talk) 20:59, 30 May 2020 (UTC)

# Palindrome detection

Palindrome detection
You are encouraged to solve this task according to the task description, using any language you may know.

A palindrome is a phrase which reads the same backward and forward.

Write a function or program that checks whether a given sequence of characters (or, if you prefer, bytes) is a palindrome.

For extra credit:

• Support Unicode characters.
• Write a second function (possibly as a wrapper to the first) which detects inexact palindromes, i.e. phrases that are palindromes if white-space and punctuation is ignored and case-insensitive comparison is used.
Hints

## 11l

Translation of: Python
`F is_palindrome(s)   R s == reversed(s)`

## 360 Assembly

`*        Reverse b string          25/06/2018PALINDRO CSECT         USING  PALINDRO,R13       base register         B      72(R15)            skip savearea         DC     17F'0'             savearea         STM    R14,R12,12(R13)    prolog         ST     R13,4(R15)         "         ST     R15,8(R13)         "         LR     R13,R15            "         LA     R8,BB              @b[1]         LA     R9,AA+L'AA-1       @a[n-1]         LA     R6,1               i=1LOOPI    C      R6,=A(L'AA)        do i=1 to length(a)          BH     ELOOPI             leave i         MVC    0(1,R8),0(R9)        substr(b,i,1)=substr(a,n-i+1,1)         LA     R8,1(R8)             @[email protected]+1         BCTR   R9,0                 @[email protected]         LA     R6,1(R6)             i=i+1         B      LOOPI              end doELOOPI   XPRNT  AA,L'AA            print a          CLC    BB,AA              if b=a          BNE    SKIP         XPRNT  MSG,L'MSG          then print msg SKIP     L      R13,4(0,R13)       epilog         LM     R14,R12,12(R13)    "         XR     R15,R15            "         BR     R14                exitAA       DC     CL32'INGIRUMIMUSNOCTEETCONSUMIMURIGNI'  aBB       DS     CL(L'AA)           bMSG      DC     CL23'IT IS A TRUE PALINDROME'         YREGS         END    PALINDRO`
Output:
```INGIRUMIMUSNOCTEETCONSUMIMURIGNI
IT IS A TRUE PALINDROME
```

## 8080 Assembly

`	org	100h	jmp	demo	;;;	Is the \$-terminated string at DE a palindrome?	;;;	Returns: zero flag set if palindromepalin:	mov	h,d	; Find end of string	mov	l,e	mvi	a,'\$'	cmp	m	; The empty string is a palindrome	rzpend:	inx	h	; Scan until terminator found	cmp	m	jnz	pend	dcx	h	; Move to last byte of textptest:	ldax	d	; Load char at left pointer	cmp 	m	; Compare to char at right pointer	rnz		; If not equal, not a palindrome	inx	d	; Move pointers	dcx	h	mov	a,d	; Check if left pointer is before right pointer	cmp 	h	; High byte	jc	ptest	mov	a,e	; Low byte	cmp	l	jc	ptest	xra	a	; Made it to the end - set zero flag	ret		; Return	;;;	Test the routine on a few examplesdemo:	lxi	h,words	; Word list pointerloop:	mov	e,m	; Load word pointer	inx	h	mov	d,m	inx	h	mov	a,e	; Stop when zero reached	ora	d	rz	push	h	; Keep word list pointer	call	pstr	; Print word	call	palin	; Check if palindrome	lxi	d,no	jnz 	print	; Print "no" if not a palindrome	lxi	d,yes	; Print "yes" otherwiseprint:	call	pstr	pop	h	jmp 	loop	;;;	Print strint using CP/M keeping DEHL registerspstr:	push	d	push	h	mvi	c,9	call	5	pop	h	pop	d	ret yes:	db	': yes',13,10,'\$'no:	db	': no',13,10,'\$'	words:	dw	w1,w2,w3,w4,0w1:	db	'rotor\$'w2:	db	'racecar\$'w3:	db	'level\$'w4:	db	'rosetta\$'`
Output:
```rotor: yes
racecar: yes
level: yes
rosetta: no```

## 8086 Assembly

`	cpu	8086	org	100hsection	.text	jmp	demo	;;;	Check if the \$-terminated string in [DS:SI] is a palindrome.	;;;	Returns with zero flag set if so.	;;;	Destroyed: AL, CX, SI, DI, ES. palin:	push	es		; Set ES=DS.	pop	ds	mov	al,'\$'		; Find end of string	mov	cx,-1	mov	di,si	repne	scasb	dec	di		; Move back to last actual character.loop:	cmp	si,di	ja	.ok		; If SI > DI, it is a palindrome	lodsb	dec	di		; Compare left character to right character	cmp	al,[di]	jne	.no		; If not equal, not a palindrome	jmp 	.loop		; Otherwise, try next pair of characters.ok:	cmp	al,al		; Set zero flag.no: 	ret 			; Return	;;;	Try the routine on a couple of stringsdemo:	mov	si,words.loop:	lodsw			; Grab word pointer	test	ax,ax		; Zero?	jz	.done		; Then we are done	mov	dx,ax		; Otherwise, print word	mov	ah,9			int	21h	xchg	bp,si		; Keep array pointer in BP	xchg	si,dx		; Put word pointer in SI	call	palin		; Check if it is a palindrome	mov	dx,yes		; Print 'yes'...	jz	.print		; ...if it is a palindrome	mov	dx,no		; Otherwise, print 'no'.print:	int 	21h	xchg	si,bp		; Restore array pointer	jmp	.loop		; Get next word..done:	retyes:	db	': yes',13,10,'\$'	; Yes and nono:	db	': no',13,10,'\$'words:	dw	.w1,.w2,.w3,.w4,.w5,0.w1:	db	'rotor\$'	; Words to check.w2:	db	'racecar\$'.w3:	db	'level\$'.w4:	db	'redder\$'.w5:	db	'rosetta\$'`
Output:
```rotor: yes
racecar: yes
level: yes
redder: yes
rosetta: no```

## ACL2

`(defun reverse-split-at-r (xs i ys)  (if (zp i)      (mv xs ys)      (reverse-split-at-r (rest xs) (1- i)                          (cons (first xs) ys)))) (defun reverse-split-at (xs i)  (reverse-split-at-r xs i nil)) (defun is-palindrome (str)  (let* ((lngth (length str))         (idx (floor lngth 2)))    (mv-let (xs ys)            (reverse-split-at (coerce str 'list) idx)            (if (= (mod lngth 2) 1)                (equal (rest xs) ys)                (equal xs ys)))))`

## Action!

`BYTE FUNC Palindrome(CHAR ARRAY s)  BYTE l,r   l=1 r=s(0)  WHILE l<r  DO    IF s(l)#s(r) THEN RETURN (0) FI    l==+1 r==-1  ODRETURN (1) BYTE FUNC IsIgnored(BYTE c)  IF (c>='  AND c<='/) OR     (c>=': AND c<='@) OR     (c>='[ AND c<='_) THEN    RETURN (1)  FI  RETURN (0) BYTE FUNC ToUpper(BYTE c)  IF c>='a AND c<='z THEN    RETURN (c-'a+'A)  FIRETURN (c) BYTE FUNC InexactPalindrome(CHAR ARRAY s)  BYTE l,r,lc,rc   l=1 r=s(0)  WHILE l<r  DO    WHILE IsIgnored(s(l))    DO      l==+1      IF l>=r THEN RETURN (1) FI    OD    WHILE IsIgnored(s(r))    DO      r==-1      IF l>=r THEN RETURN (1) FI    OD     lc=ToUpper(s(l))    rc=ToUpper(s(r))     IF lc#rc THEN RETURN (0) FI    l==+1 r==-1  ODRETURN (1) PROC Test(CHAR ARRAY s)  IF Palindrome(s) THEN    PrintF("'%S' is a palindrome%E%E",s)  ELSEIF InexactPalindrome(s) THEN    PrintF("'%S' is an inexact palindrome%E%E",s)  ELSE    PrintF("'%S' is not a palindrome%E%E",s)  FIRETURN PROC Main()  Test("rotavator")  Test("13231+464+989=989+464+13231")  Test("Was it a car or a cat I saw?")  Test("Did Hannah see bees? Hannah did.")  Test("This sentence is not a palindrome.")  Test("123 456 789 897 654 321")RETURN`
Output:
```'rotavator' is a palindrome

'13231+464+989=989+464+13231' is a palindrome

'Was it a car or a cat I saw?' is an inexact palindrome

'Did Hannah see bees? Hannah did.' is an inexact palindrome

'This sentence is not a palindrome.' is not a palindrome

'123 456 789 897 654 321' is not a palindrome
```

## ActionScript

The following function handles non-ASCII characters properly, since charAt() returns a single Unicode character.

`function isPalindrome(str:String):Boolean{	for(var first:uint = 0, second:uint = str.length - 1; first < second; first++, second--)		if(str.charAt(first) != str.charAt(second)) return false;	return true;}`

`function Palindrome (Text : String) return Boolean isbegin   for Offset in 0..Text'Length / 2 - 1 loop      if Text (Text'First + Offset) /= Text (Text'Last - Offset) then         return False;      end if;   end loop;   return True;end Palindrome;`

` function Palindrome (Text : String) return Boolean is(for all i in Text'Range => Text(i)= Text(Text'Last-i+Text'First)); `

## ALGOL 68

Translation of: C
Works with: ALGOL 68 version Standard - no extensions to language used
Works with: ALGOL 68G version Any - tested with release mk15-0.8b.fc9.i386
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8.8d.fc9.i386 - except for the FORMAT and printf in test
`# Iterative #PROC palindrome = (STRING s)BOOL:(   FOR i TO UPB s OVER 2 DO     IF s[i] /= s[UPB s-i+1] THEN GO TO return false FI   OD;Power   else: TRUE EXIT   return false: FALSE); # Recursive #PROC palindrome r = (STRING s)BOOL:   IF LWB s >= UPB s THEN TRUE   ELIF s[LWB s] /= s[UPB s] THEN FALSE   ELSE palindrome r(s[LWB s+1:UPB s-1])   FI; # Test #main:(   STRING t = "ingirumimusnocteetconsumimurigni";   FORMAT template = \$"sequence """g""" "b("is","isnt")" a palindrome"l\$;    printf((template, t, palindrome(t)));   printf((template, t, palindrome r(t))))`
Output:
```sequence "ingirumimusnocteetconsumimurigni" is a palindrome
sequence "ingirumimusnocteetconsumimurigni" is a palindrome
```

## APL

NARS2000 APL, dynamic function "if the argument matches the reverse of the argument", with Unicode character support:

`      {⍵≡⌽⍵} 'abc'0      {⍵≡⌽⍵} '⍋racecar⍋'1`

Or in tacit function form, a combination of three functions, right tack (echo), reverse, then the result of each compared with the middle one, match (equals):

`      (⊢≡⌽) 'abc'0      (⊢≡⌽) 'nun'1`

An inexact version is harder, because uppercase and lowercase with Unicode awareness depends on APL interpreter; NARS2000 has no support for it. Classic case conversion means lookup up the letters in an alphabet of UppercaseLowercase, then mapping those positions into an UppercaseUppercase or LowercaseLowercase array. Remove non-A-Za-z first to get rid of punctuation, and get an inexact dynamic function with just English letter support:

`inexact←{Aa←(⎕A,⎕a) ⋄ (⊢≡⌽)(⎕a,⎕a)[Aa⍳⍵/⍨⍵∊Aa]}      inexact 'abc,-cbA2z'0      inexact 'abc,-cbA2'1`

Dyalog APL has a Unicode-aware uppercase/lowercase function (819 I-beam), AFAIK no support for looking up Unicode character classes.

## AppleScript

Using post-Yosemite AppleScript (to pull in lowercaseStringWithLocale from Foundation classes)

`use framework "Foundation" ------ CASE-INSENSITIVE PALINDROME, IGNORING SPACES ? ---- -- isPalindrome :: String -> Boolon isPalindrome(s)    s = intercalate("", reverse of characters of s)end isPalindrome -- toSpaceFreeLower :: String -> Stringon spaceFreeToLower(s)    script notSpace        on |λ|(s)            s is not space        end |λ|    end script     intercalate("", filter(notSpace, characters of toLower(s)))end spaceFreeToLower  --------------------------- TEST -------------------------on run     isPalindrome(spaceFreeToLower("In girum imus nocte et consumimur igni"))     --> true end run  -------------------- GENERIC FUNCTIONS ------------------- -- filter :: (a -> Bool) -> [a] -> [a]on filter(f, xs)    tell mReturn(f)        set lst to {}        set lng to length of xs        repeat with i from 1 to lng            set v to item i of xs            if |λ|(v, i, xs) then set end of lst to v        end repeat        return lst    end tellend filter  -- intercalate :: Text -> [Text] -> Texton intercalate(strText, lstText)    set {dlm, my text item delimiters} to {my text item delimiters, strText}    set strJoined to lstText as text    set my text item delimiters to dlm    return strJoinedend intercalate  -- Lift 2nd class handler function into 1st class script wrapper -- mReturn :: Handler -> Scripton mReturn(f)    if class of f is script then        f    else        script            property |λ| : f        end script    end ifend mReturn  -- toLower :: String -> Stringon toLower(str)    set ca to current application    ((ca's NSString's stringWithString:(str))'s ¬        lowercaseStringWithLocale:(ca's NSLocale's currentLocale())) as textend toLower`
Output:
`true`

### Core language only

It's not clear if "sequence of characters" means an array thereof or a single piece of text. But the basic method in AppleScript would be:

`on isPalindrome(txt)    set txt to join(txt, "") -- In case the input's a list (array).    return (txt = join(reverse of txt's characters, ""))end isPalindrome on join(lst, delim)    set astid to AppleScript's text item delimiters    set AppleScript's text item delimiters to delim    set txt to lst as text    set AppleScript's text item delimiters to astid    return txtend join return isPalindrome("Radar")`

Text comparisons in AppleScript are case-insensitive by default, so:

Output:
`true`

If case is to be taken into account, the call to the handler can be enclosed in a 'considering case' control statement.

`considering case    return isPalindrome("Radar")end considering`
Output:
`false`

It's also possible to "ignore" white space, hyphens, and punctuation, which are considered by default. And of course case can be ignored explicitly, if desired, to ensure that this condition's in force during the call to the handler. The attributes can be combined in one statement. So to check for inexact palindromicity (if that's a word):

`ignoring case, white space, hyphens and punctuation    return isPalindrome("Was it a 😀car, or a c😀at-I-saw?")end ignoring`
Output:
`true`

## Applesoft BASIC

`100 DATA"MY DOG HAS FLEAS"110 DATA"MADAM, I'M ADAM."120 DATA"1 ON 1"130 DATA"IN GIRUM IMUS NOCTE ET CONSUMIMUR IGNI"140 DATA"A man, a plan, a canal: Panama!"150 DATA"KAYAK"160 DATA"REDDER"170 DATA"H"180 DATA"" 200 FOR L1 = 1 TO 9210    READ W\$ : GOSUB 300" IS PALINDROME?220    PRINT CHR\$(34); W\$; CHR\$(34); " IS ";230    IF NOT PALINDROME THEN PRINT "NOT ";240    PRINT "A PALINDROME"250 NEXT260 END 300 REMIS PALINDROME?310 PA = 1320 L = LEN(W\$)330 IF L = 0 THEN RETURN340 FOR L0 = 1 TO L / 2 + .5350     PA = MID\$(W\$, L0, 1) = MID\$(W\$, L - L0 + 1, 1)360     IF PALINDROME THEN NEXT L0370 RETURN`

## ARM Assembly

`@ Check whether the ASCII string in [r0] is a palindrome@ Returns with zero flag set if palindrome.palin:	mov	r1,r0		@ Find end of string1:	ldrb	r2,[r1],#1	@ Grab character and increment pointer	tst	r2,r2		@ Zero yet?	bne	1b		@ If not try next byte	sub	r1,r1,#2	@ Move R1 to last actual character.2:	cmp	r0,r1		@ When R0 >= R1,	cmpgt	r2,r2		@ make sure zero is set,	bxeq	lr		@ and stop (the string is a palindrome).	ldrb	r2,[r1],#-1	@ Grab [R1] (end) and decrement.	ldrb	r3,[r0],#1	@ Grab [R0] (begin) and increment	cmp	r2,r3		@ Are they equal?	bxne	lr		@ If not, it's not a palindrome.	b	2b		@ Otherwise, try next pair. @ Try the function on a couple of strings.global _start_start:	ldr	r8,=words	@ Word pointer1:	ldr	r9,[r8],#4	@ Grab word and move pointer	tst	r9,r9		@ Null?	moveq	r7,#1		@ Then we're done; syscall 1 = exit	swieq	#0	mov	r1,r9		@ Print the word	bl	print			mov	r0,r9		@ Test if the word is a palindrome	bl	palin	ldreq	r1,=yes		@ "Yes" if it is a palindrome	ldrne	r1,=no		@ "No" if it's not a palindrome	bl	print	b	1b		@ Next word  @ Print zero-terminated string [r1] using Linux syscallprint:	push	{r7,lr}		@ Keep R7 and link register	mov	r2,r1		@ Find end of string1:	ldrb	r0,[r2],#1	@ Grab character and increment pointer	tst	r0,r0		@ Zero yet?	bne	1b		@ If not, keep going	sub	r2,r2,r1	@ Calculate length of string (bytes to write)	mov	r0,#1		@ Stdout = 1	mov	r7,#4		@ Syscall 4 = write	swi	#0		@ Make the syscall	pop	{r7,lr}		@ Restore R7 and link register	bx	lr @ Stringsyes:	.asciz	": yes\n"	@ Output yes or nono:	.asciz	": no\n"w1:	.asciz	"rotor"		@ Words to testw2:	.asciz	"racecar"w3:	.asciz	"level"w4:	.asciz	"redder"w5:	.asciz	"rosetta"words:	.word	w1,w2,w3,w4,w5,0`
Output:
```rotor: yes
racecar: yes
level: yes
redder: yes
rosetta: no```

## Arturo

`palindrome?: \$[seq] -> seq = reverse seq loop ["abba" "boom" "radar" "civic" "great"] 'wrd [	print [wrd ": palindrome?" palindrome? wrd]]`
Output:
```abba : palindrome? true
boom : palindrome? false
civic : palindrome? true
great : palindrome? false```

## AutoHotkey

Reversing the string:

`IsPalindrome(Str){	Loop, Parse, Str		ReversedStr := A_LoopField . ReversedStr	return, (ReversedStr == Str)?"Exact":(RegExReplace(ReversedStr,"\W")=RegExReplace(Str,"\W"))?"Inexact":"False"}`

## AutoIt

`;== AutoIt Version: 3.3.8.1 Global \$aString[7] = [ _"In girum imus nocte, et consumimur igni", _  ; inexact palindrome"Madam, I'm Adam.", _                         ; inexact palindrome"salàlas", _                                  ; exact palindrome"radar", _                                    ; exact palindrome"Lagerregal", _                               ; exact palindrome"Ein Neger mit Gazelle zagt im Regen nie.", _ ; inexact palindrome"something wrong"]                            ; no palindromeGlobal \$sSpace42 = "                                          " For \$i = 0 To 6	If _IsPalindrome(\$aString[\$i]) Then		ConsoleWrite('"' & \$aString[\$i] & '"' & StringLeft(\$sSpace42, 42-StringLen(\$aString[\$i])) & 'is an exact palindrome.' & @LF)	Else		If _IsPalindrome( StringRegExpReplace(\$aString[\$i], '\W', '') ) Then			ConsoleWrite('"' & \$aString[\$i] & '"' & StringLeft(\$sSpace42, 42-StringLen(\$aString[\$i])) & 'is an  inexact palindrome.' & @LF)		Else			ConsoleWrite('"' & \$aString[\$i] & '"' & StringLeft(\$sSpace42, 42-StringLen(\$aString[\$i])) & 'is not a palindrome.' & @LF)		EndIf	EndIfNext Func _IsPalindrome(\$_string)	Local \$iLen = StringLen(\$_string)	For \$i = 1  To Int(\$iLen/2)		If StringMid(\$_string, \$i, 1) <> StringMid(\$_string, \$iLen-(\$i-1), 1) Then Return False	Next	Return TrueEndFunc `
Output:
` "In girum imus nocte, et consumimur igni"   is an inexact palindrome."Madam, I'm Adam."                          is an inexact palindrome."salàlas"                                   is an exact palindrome."radar"                                     is an exact palindrome."Lagerregal"                                is an exact palindrome."Ein Neger mit Gazelle zagt im Regen nie."  is an inexact palindrome."something wrong"                           is not a palindrome. `

--BugFix (talk) 14:26, 13 November 2013 (UTC)

## AWK

Non-recursive

`function is_palindro(s){  if ( s == reverse(s) ) return 1  return 0}`

Recursive

`function is_palindro_r(s){  if ( length(s) < 2 ) return 1  if ( substr(s, 1, 1) != substr(s, length(s), 1) ) return 0  return is_palindro_r(substr(s, 2, length(s)-2))}`

Testing

`BEGIN {  pal = "ingirumimusnocteetconsumimurigni"  print is_palindro(pal)  print is_palindro_r(pal)}`

## BaCon

` OPTION COMPARE TRUE INPUT "Enter your line... ", word\$ IF word\$ = REVERSE\$(word\$) THEN    PRINT "This is an exact palindrome!"ELIF EXTRACT\$(word\$, "[[:punct:]]|[[:blank:]]", TRUE) = REVERSE\$(EXTRACT\$(word\$, "[[:punct:]]|[[:blank:]]", TRUE)) THEN    PRINT "This is an inexact palindrome!"ELSE    PRINT "Not a palindrome."ENDIF `
Output:
```Enter your line... In girum imus nocte, et consumimur igni
This is an inexact palindrome!
This is an inexact palindrome!
This is an exact palindrome!
Not a palindrome.
```

## Bash

` #! /bin/bash# very simple way to detect a palindrome in Bash# output of bash --version -> GNU bash, version 4.4.7(1)-release x86_64 ... echo "enter a string"read input size=\${#input}count=0 while ((\$count < \$size))do    array[\$count]=\${input:\$count:1}    (( count+=1 ))done count=0 for ((i=0 ; i < \$size; i+=1))do    if [ "\${array[\$i]}" == "\${array[\$size - \$i - 1]}" ]    then        (( count += 1 ))    fidone if (( \$count == \$size ))then    echo "\$input is a palindrome"fi `

## BASIC

Works with: QBasic
`' OPTION _EXPLICIT ' For QB64. In VB-DOS remove the underscore. DIM txt\$ ' PalindromeCLSPRINT "This is a palindrome detector program."PRINTINPUT "Please, type a word or phrase: ", txt\$ IF IsPalindrome(txt\$) THEN  PRINT "Is a palindrome."ELSE  PRINT "Is Not a palindrome."END IF END  FUNCTION IsPalindrome (AText\$)  ' Var  DIM CleanTXT\$, RvrsTXT\$   CleanTXT\$ = CleanText\$(AText\$)  RvrsTXT\$ = RvrsText\$(CleanTXT\$)   IsPalindrome = (CleanTXT\$ = RvrsTXT\$) END FUNCTION FUNCTION CleanText\$ (WhichText\$)  ' Var  DIM i%, j%, c\$, NewText\$, CpyTxt\$, AddIt%, SubsTXT\$  CONST False = 0, True = NOT False   SubsTXT\$ = "AIOUE"  CpyTxt\$ = UCASE\$(WhichText\$)  j% = LEN(CpyTxt\$)   FOR i% = 1 TO j%    c\$ = MID\$(CpyTxt\$, i%, 1)     ' See if it is a letter. Includes Spanish letters.    SELECT CASE c\$      CASE "A" TO "Z"        AddIt% = True      CASE " ", "¡", "¢", "£"        c\$ = MID\$(SubsTXT\$, ASC(c\$) - 159, 1)        AddIt% = True      CASE "‚"        c\$ = "E"        AddIt% = True      CASE "¤"        c\$ = "¥"        AddIt% = True      CASE ELSE        AddIt% = False    END SELECT     IF AddIt% THEN      NewText\$ = NewText\$ + c\$    END IF  NEXT i%   CleanText\$ = NewText\$ END FUNCTION FUNCTION RvrsText\$ (WhichText\$)  ' Var  DIM i%, c\$, NewText\$, j%   j% = LEN(WhichText\$)  FOR i% = 1 TO j%    NewText\$ = MID\$(WhichText\$, i%, 1) + NewText\$  NEXT i%   RvrsText\$ = NewText\$ END FUNCTION`
Output:

This is a palindrome detector program.

This is a palindrome detector program.

Please, type a word or phrase: This is just a test. Is not a palindrome.

### IS-BASIC

` 100 PROGRAM "Palindr.bas"110 LINE INPUT PROMPT "Text: ":TX\$120 PRINT """";TX\$;""" is ";130 IF PALIND(TX\$) THEN140   PRINT "a palindrome."150 ELSE160   PRINT "not a palindrome."170 END IF180 DEF TRIM\$(TX\$)190   LET T\$=""200   FOR I=1 TO LEN(TX\$)210     IF TX\$(I)>="A" AND TX\$(I)<="Z" THEN LET T\$=T\$&TX\$(I)220   NEXT230   LET TRIM\$=T\$240 END DEF250 DEF PALIND(TX\$)260   LET PALIND=-1:LET TX\$=TRIM\$(UCASE\$(TX\$))270   FOR I=1 TO LEN(TX\$)/2280     IF TX\$(I)<>TX\$(LEN(TX\$)-I+1) THEN LET PALIND=0:EXIT FOR290   NEXT300 END DEF`

### Sinclair ZX81 BASIC

#### Exact palindrome

The specification suggests, but does not insist, that we reverse the input string and then test for equality; this algorithm is more efficient.

` 10 INPUT S\$ 20 FOR I=1 TO LEN S\$/2 30 IF S\$(I)<>S\$(LEN S\$-I+1) THEN GOTO 60 40 NEXT I 50 GOTO 70 60 PRINT "NOT A "; 70 PRINT "PALINDROME"`

#### Inexact palindrome

Add the following lines to convert the program into an inexact-palindrome checker (i.e. one that ignores non-alphabetic characters). The resulting program still works with only 1k of RAM. The ZX81 only supports its own character set, which does not include lower case, so that case-insensitive comparison and a fortiori Unicode are not possible.

` 15 GOSUB 90 80 STOP 90 LET T\$=""100 FOR I=1 TO LEN S\$110 IF S\$(I)>="A" AND S\$(I)<="Z" THEN LET T\$=T\$+S\$(I)120 NEXT I130 LET S\$=T\$140 RETURN`

### BBC BASIC

`      test\$ = "A man, a plan, a canal: Panama!"      PRINT """" test\$ """" ;      IF FNpalindrome(FNletters(test\$)) THEN        PRINT " is a palindrome"      ELSE        PRINT " is not a palindrome"      ENDIF      END       DEF FNpalindrome(A\$) = (A\$ = FNreverse(A\$))       DEF FNreverse(A\$)      LOCAL B\$, P%      FOR P% = LEN(A\$) TO 1 STEP -1        B\$ += MID\$(A\$,P%,1)      NEXT      = B\$       DEF FNletters(A\$)      LOCAL B\$, C%, P%      FOR P% = 1 TO LEN(A\$)        C% = ASC(MID\$(A\$,P%))        IF C% > 64 AND C% < 91 OR C% > 96 AND C% < 123 THEN          B\$ += CHR\$(C% AND &5F)        ENDIF      NEXT      = B\$`
Output:
`"A man, a plan, a canal: Panama!" is a palindrome`

## Batch File

`@echo offsetlocal enabledelayedexpansionset /p string=Your string :set count=0:loop	if "!%string%:~%count%,1!" neq "" (		set reverse=!%string%:~%count%,1!!reverse!		set /a count+=1		goto loop	)set palindrome=isn'tif "%string%"=="%reverse%" set palindrome=isecho %string% %palindrome% a palindrome.pauseexit`

Or, recursive (and without setlocal enabledelayedexpansion) (compatible with ReactOS cmd.exe)

`@echo offset /p testString=Your string (all same case please) : call :isPalindrome result %testString: =%if %result%==1 echo %testString% is a palindromeif %result%==0 echo %testString% isn't a palindromepausegoto :eof :isPalindrome	set %1=0	set string=%2	if "%string:~2,1%"=="" (		set %1=1		goto :eof	)	if "%string:~0,1%"=="%string:~-1%" (		call :isPalindrome %1 %string:~1,-1%	)	goto :eof`

## BCPL

`get "libhdr" let palindrome(s) = valof\$(  let l = s%0    for i = 1 to l/2        unless s%i = s%(l+1-i)             resultis false    resultis true\$) let inexact(s) = valof\$(  let temp = vec 1+256/BYTESPERWORD    temp%0 := 0    for i = 1 to s%0 do    \$(  let ch = s%i | 32        if '0'<=ch & ch<='9' | 'a'<=ch & ch<='z' then        \$(  temp%0 := temp%0 + 1            temp%(temp%0) := ch        \$)    \$)    resultis palindrome(temp)\$) let check(s) =    palindrome(s) -> "exact palindrome",    inexact(s) -> "inexact palindrome",    "not a palindrome" let start() be \$(  let tests = vec 8    tests!0 := "rotor"    tests!1 := "racecar"    tests!2 := "RACEcar"    tests!3 := "level"    tests!4 := "redder"    tests!5 := "rosetta"    tests!6 := "A man, a plan, a canal: Panama"    tests!7 := "Egad, a base tone denotes a bad age"    tests!8 := "This is not a palindrome"     for i = 0 to 8 do        writef("'%S': %S*N", tests!i, check(tests!i))\$)`
Output:
```'rotor': exact palindrome
'racecar': exact palindrome
'RACEcar': inexact palindrome
'level': exact palindrome
'redder': exact palindrome
'rosetta': not a palindrome
'A man, a plan, a canal: Panama': inexact palindrome
'This is not a palindrome': not a palindrome```

## Befunge

Works with: CCBI version 2.1

The following code reads a line from stdin and prints "True" if it is a palindrome, or False" otherwise.

`v_\$0:8p>:#v_:18p08g1-08p >:08g`!v~->p5p ^  0v1p80-1g80vj!-g5g80g5_0'ev:a^80+1:g8<>8g1+:18pv>0"eslaF">:#,[email protected] [[relet]]-2010------>003-x   -^"Tru"<`
Works with: Befunge version 93

To check a string, replace "dennis sinned" with your own string.

Note that this has some limits.:

• There must be a quotation mark immediately after the string, and then nothing but spaces for the rest of that line.
• The v at the end of that same line must remain immediately above the 2. (Very important.) The closing quotation mark can be against the v, but can't replace it.
• The potential palindrome can be no longer than 76 characters (which beats the previous version's 11), and everything (spaces, punctuation, capitalization, etc.) is considered part of the palindrome. (Best to just use lower case letters and nothing else.)
`v>    "emordnilap a toN",,,,,,,,,,,,,,,,@,,,,,,,,,,,,,,,"Is a palindrome"     <2^ < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < <4    ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v8  ^_v # ^_v # ^_v # ^_v # ^_v # ^_v # ^_v # ^_v # ^_v # ^_v # ^_v # ^_v # ^_v*^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v   ^_v+ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""">"dennis sinned"                                                               v "                                                                             2  """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 0> ^- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9   _^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^  p    v_^ # v_^ # v_^ # v_^ # v_^ # v_^ # v_^ # v_^ # v_^ # v_^ # v_^ # v_^ # v_^      v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^   v_^ ^< < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < >09g8p09g1+09pv |:            <                                                               <^<`

## BQN

3 functions in three different styles to check if a string is a palindrome. All three forms return 1 for palindrome, and 0 for non-palindrome.

BQN considers characters as single units, and hence the functions support unicode by default.

`Pal ← ≡⊸⌽Pal1 ← ⊢≡⌽Pal2 ← {𝕩≡⌽𝕩}`

## Bracmat

`( ( palindrome  =   a    .     @(!arg:(%?a&utf\$!a) ?arg !a)        & palindrome\$!arg      | utf\$!arg  )& ( desep  =   x    .     @(!arg:?x (" "|"-"|",") ?arg)        & !x desep\$!arg      | !arg  )&     "In girum imus nocte et consumimur igni"      "Я иду с мечем, судия"      "The quick brown fox"      "tregða, gón, reiði - er nóg að gert"      "人人為我,我為人人"      "가련하시다 사장집 아들딸들아 집장사 다시 하련가"  : ?candidates&   whl  ' ( !candidates:%?candidate ?candidates    &   out      \$ ( !candidate          is          (   palindrome\$(low\$(str\$(desep\$!candidate)))            & indeed          | not          )          a          palindrome        )    )&);`

Output:

```In girum imus nocte et consumimur igni is indeed a palindrome
Я иду с мечем, судия is indeed a palindrome
The quick brown fox is not a palindrome
tregða, gón, reiði - er nóg að gert is indeed a palindrome

가련하시다 사장집 아들딸들아 집장사 다시 하련가
is
indeed
a
palindrome
```

## Burlesque

` zz{ri}f[^^<-== `

## C

Non-recursive

This function compares the first char with the last, the second with the one previous the last, and so on. The first different pair it finds, return 0 (false); if all the pairs were equal, then return 1 (true). You only need to go up to (the length) / 2 because the second half just re-checks the same stuff as the first half; and if the length is odd, the middle doesn't need to be checked (so it's okay to do integer division by 2, which rounds down).

`#include <string.h> int palindrome(const char *s){   int i,l;   l = strlen(s);   for(i=0; i<l/2; i++)   {     if ( s[i] != s[l-i-1] ) return 0;    }   return 1;}`

More idiomatic version:

`int palindrome(const char *s){   const char *t; /* t is a pointer that traverses backwards from the end */   for (t = s; *t != '\0'; t++) ; t--; /* set t to point to last character */   while (s < t)   {     if ( *s++ != *t-- ) return 0;    }   return 1;}`

Recursive

A single char is surely a palindrome; a string is a palindrome if first and last char are the same and the remaining string (the string starting from the second char and ending to the char preceding the last one) is itself a palindrome.

`int palindrome_r(const char *s, int b, int e){   if ( (e - 1) <= b ) return 1;   if ( s[b] != s[e-1] ) return 0;   return palindrome_r(s, b+1, e-1);}`

Testing

`#include <stdio.h>#include <string.h>/* testing */int main(){   const char *t = "ingirumimusnocteetconsumimurigni";   const char *template = "sequence \"%s\" is%s palindrome\n";   int l = strlen(t);    printf(template,          t, palindrome(t) ? "" : "n't");   printf(template,          t, palindrome_r(t, 0, l) ? "" : "n't");   return 0;}`

## C#

Non-recursive

`using System; class Program{    static string Reverse(string value)    {        char[] chars = value.ToCharArray();        Array.Reverse(chars);        return new string(chars);    }     static bool IsPalindrome(string value)    {        return value == Reverse(value);    }     static void Main(string[] args)    {        Console.WriteLine(IsPalindrome("ingirumimusnocteetconsumimurigni"));    }}`

Using LINQ operators

`using System;using System.Linq; class Program{	static bool IsPalindrome(string text)	{		return text == new String(text.Reverse().ToArray());	} 	static void Main(string[] args)	{		Console.WriteLine(IsPalindrome("ingirumimusnocteetconsumimurigni"));	}} `

No string reversal

Reversing a string is very slow. A much faster way is to simply compare characters.

`using System; static class Program{    //As an extension method (must be declared in a static class)    static bool IsPalindrome(this string sentence)    {        for (int l = 0, r = sentence.Length - 1; l < r; l++, r--)            if (sentence[l] != sentence[r]) return false;        return true;    }     static void Main(string[] args)    {        Console.WriteLine("ingirumimusnocteetconsumimurigni".IsPalindrome());    }}`

## C++

The C solutions also work in C++, but C++ allows a simpler one:

`#include <string>#include <algorithm> bool is_palindrome(std::string const& s){  return std::equal(s.begin(), s.end(), s.rbegin());}`

Or, checking half is sufficient (on odd-length strings, this will ignore the middle element):

`#include <string>#include <algorithm> bool is_palindrome(std::string const& s){  return std::equal(s.begin(), s.begin()+s.length()/2, s.rbegin());}`

## Clojure

`(defn palindrome? [s]  (= s (clojure.string/reverse s)))`

lower-level, but somewhat faster

`(defn palindrome? [^String s]  (loop [front 0 back (dec (.length s))]    (or (>= front back)        (and (= (.charAt s front) (.charAt s back))             (recur (inc front) (dec back)))))`

Test

```user=> (palindrome? "amanaplanacanalpanama")
true
user=> (palindrome? "Test 1, 2, 3")
false
```

## CLU

`% Reverse a stringstr_reverse = proc (s: string) returns (string)    chs: array[char] := array[char]\$predict(0, string\$size(s))    for c: char in string\$chars(s) do        array[char]\$addl(chs, c)    end    return (string\$ac2s(chs))end str_reverse % 'Normalize' a string (remove everything but letters and make uppercase)normalize = proc (s: string) returns (string)    chs: array[char] := array[char]\$predict(0, string\$size(s))    for c: char in string\$chars(s) do        if c>='a' cand c<='z' then            c := char\$i2c(char\$c2i(c) - 32)        end        if c>='A' cand c<='Z' then            array[char]\$addh(chs, c)        end    end    return (string\$ac2s(chs))end normalize % Check if a string is an exact palindromepalindrome = proc (s: string) returns (bool)    return (s = str_reverse(s))end palindrome % Check if a string is an inexact palindromeinexact_palindrome = proc (s: string) returns (bool)    return (palindrome(normalize(s)))end inexact_palindrome % Test casesstart_up = proc ()    po: stream := stream\$primary_output()    tests: array[string] := array[string]\$[        "rotor", "racecar", "RACEcar", "level", "rosetta",        "A man, a plan, a canal: Panama",        "Egad, a base tone denotes a bad age",        "This is not a palindrome"    ]     for test: string in array[string]\$elements(tests) do        stream\$puts(po, "\"" || test || "\": ")        if palindrome(test) then            stream\$putl(po, "exact palindrome")        elseif inexact_palindrome(test) then            stream\$putl(po, "inexact palindrome")         else            stream\$putl(po, "not a palindrome")        end    endend start_up`
Output:
```"rotor": exact palindrome
"racecar": exact palindrome
"RACEcar": inexact palindrome
"level": exact palindrome
"rosetta": not a palindrome
"A man, a plan, a canal: Panama": inexact palindrome
"This is not a palindrome": not a palindrome```

## COBOL

Works with: GnuCOBOL
`       identification division.       function-id. palindromic-test.        data division.       linkage section.       01 test-text            pic x any length.       01 result               pic x.          88 palindromic       value high-value                               when set to false low-value.        procedure division using test-text returning result.        set palindromic to false       if test-text equal function reverse(test-text) then           set palindromic to true       end-if        goback.       end function palindromic-test. `

## CoffeeScript

`     String::isPalindrome = ->        for i in [0...@length / 2] when @[i] isnt @[@length - (i + 1)]            return no        yes     String::stripped = -> @toLowerCase().replace /\W/gi, ''     console.log "'#{ str }' : #{ str.stripped().isPalindrome() }" for str in [        'In girum imus nocte et consumimur igni'        'A man, a plan, a canal: Panama!'        'There is no spoon.'    ] `
Output:
```   'In girum imus nocte et consumimur igni' : true
'A man, a plan, a canal: Panama!' : true
'There is no spoon.' : false
```

## Common Lisp

`(defun palindrome-p (s)  (string= s (reverse s)))`

### Alternate solution

I use Allegro CL 10.1

` ;; Project : Palindrome detection (defun palindrome(x)          (if (string= x (reverse x))          (format t "~d" ": palindrome" (format t x))          (format t "~d" ": not palindrome" (format t x))))         (terpri)(setq x "radar")(palindrome x)(terpri)(setq x "books")(palindrome x)(terpri) `

Output:

```radar: palindrome
books: not palindrome
```

## Component Pascal

BlackBox Component Builder

` MODULE BbtPalindrome;IMPORT StdLog; PROCEDURE ReverseStr(str: ARRAY OF CHAR): POINTER TO ARRAY OF CHAR;VAR	top,middle,i: INTEGER;	c: CHAR;	rStr: POINTER TO ARRAY OF CHAR;BEGIN	NEW(rStr,LEN(str\$) + 1);	top := LEN(str\$) - 1; middle := (top - 1) DIV 2;	FOR i := 0 TO middle DO		rStr[i] := str[top - i];		rStr[top - i] := str[i];	END;	IF ODD(LEN(str\$)) THEN rStr[middle + 1] := str[middle + 1] END;	RETURN rStr;END ReverseStr; PROCEDURE IsPalindrome(str: ARRAY OF CHAR): BOOLEAN;BEGIN	RETURN str = ReverseStr(str)\$;END IsPalindrome; PROCEDURE Do*;VAR	x: CHAR;BEGIN	StdLog.String("'salalas' is palindrome?:> ");	StdLog.Bool(IsPalindrome("salalas"));StdLog.Ln;	StdLog.String("'madamimadam' is palindrome?:> ");	StdLog.Bool(IsPalindrome("madamimadam"));StdLog.Ln;	StdLog.String("'abcbda' is palindrome?:> ");	StdLog.Bool(IsPalindrome("abcbda"));StdLog.Ln;END Do;END BbtPalindrome. `

Execute: ^Q BbtPalindrome.Do

Output:
```'salalas' is palindrome?:>  \$TRUE
'abcbda' is palindrome?:>  \$FALSE
```

## Cowgol

`include "cowgol.coh"; # Check if a string is a palindromesub palindrome(word: [uint8]): (r: uint8) is    r := 1;     # empty string is a palindrome    if [word] == 0 then        return;    end if;     # find the end of the word    var end_ := word;    while [@next end_] != 0 loop        end_ := @next end_;     end loop;     # check if bytes match in both directions    while word < end_ loop        if [word] != [end_] then            r := 0;            return;        end if;        word := @next word;        end_ := @prev end_;    end loop;end sub; # Check if a string is an inexact palindromesub inexact(word: [uint8]): (r: uint8) is    var buf: uint8[256];    var ptr := &buf[0];    # filter non-letters and non-numbers    while [word] != 0 loop           var c := [word];        if (c >= 'a' and c <= 'z') or (c >= '0' and c <= '9') then            # copy lowercase letters and numbers over verbatim            [ptr] := c;            ptr := @next ptr;        elseif c >= 'A' and c <= 'Z' then            # make uppercase letters lowercase            [ptr] := c | 32;            ptr := @next ptr;        end if;        word := @next word;    end loop;    [ptr] := 0;    r := palindrome(&buf[0]);end sub; var tests: [uint8][] := {    "civic", "level", "racecar",    "A man, a plan, a canal: Panama",    "Egad, a base tone denotes a bad age",    "There is no spoon."}; var i: @indexof tests := 0;while i < @sizeof tests loop    print(tests[i]);    print(": ");    if palindrome(tests[i]) == 1 then        print("exact palindrome\n");    elseif inexact(tests[i]) == 1 then        print("inexact palindrome\n");    else        print("not a palindrome\n");    end if;    i := i + 1;end loop;`
Output:
```civic: exact palindrome
level: exact palindrome
racecar: exact palindrome
A man, a plan, a canal: Panama: inexact palindrome
There is no spoon.: not a palindrome```

## Crystal

### Declarative

` def palindrome(s)  s == s.reverseend `

### Imperative

` def palindrome_imperative(s) : Bool  mid = s.size // 2  last = s.size - 1  (0...mid).each do |i|    if s[i] != s[last - i]      return false    end  end   trueend `

Also

`def palindrome_2(s)  mid = s.size // 2  mid.times { |j| return false if s[j] != s[-1 - j] }  trueend`

Performance comparison

` require "benchmark"Benchmark.ips do |x|  x.report("declarative") { palindrome("hannah") }  x.report("imperative1") { palindrome_imperative("hannah")}  x.report("imperative2") { palindrome_2("hannah")}end `
```declarative  45.45M ( 22.00ns) (±11.16%)  32.0B/op        fastest
imperative1  35.49M ( 28.18ns) (± 2.82%)   0.0B/op   1.28× slower
imperative2  40.73M ( 24.55ns) (± 3.82%)   0.0B/op   1.12× slower```

## D

### High-level 32-bit Unicode Version

`import std.traits, std.algorithm; bool isPalindrome1(C)(in C[] s) pure /*nothrow*/if (isSomeChar!C) {    auto s2 = s.dup;    s2.reverse(); // works on Unicode too, not nothrow.    return s == s2;} void main() {    alias pali = isPalindrome1;    assert(pali(""));    assert(pali("z"));    assert(pali("aha"));    assert(pali("sees"));    assert(!pali("oofoe"));    assert(pali("deified"));    assert(!pali("Deified"));    assert(pali("amanaplanacanalpanama"));    assert(pali("ingirumimusnocteetconsumimurigni"));    assert(pali("salÃ las"));}`

### Mid-level 32-bit Unicode Version

`import std.traits; bool isPalindrome2(C)(in C[] s) pure if (isSomeChar!C) {    dchar[] dstr;    foreach (dchar c; s) // not nothrow        dstr ~= c;     for (int i; i < dstr.length / 2; i++)        if (dstr[i] != dstr[\$ - i - 1])            return false;    return true;} void main() {    alias isPalindrome2 pali;    assert(pali(""));    assert(pali("z"));    assert(pali("aha"));    assert(pali("sees"));    assert(!pali("oofoe"));    assert(pali("deified"));    assert(!pali("Deified"));    assert(pali("amanaplanacanalpanama"));    assert(pali("ingirumimusnocteetconsumimurigni"));    assert(pali("salÃ las"));}`

### Low-level 32-bit Unicode Version

`import std.stdio, core.exception, std.traits; // assume alloca() to be pure for this programextern(C) pure nothrow void* alloca(in size_t size); bool isPalindrome3(C)(in C[] s) pure if (isSomeChar!C) {    auto p = cast(dchar*)alloca(s.length * 4);    if (p == null)        // no fallback heap allocation used        throw new OutOfMemoryError();    dchar[] dstr = p[0 .. s.length];     // use std.utf.stride for an even lower level version    int i = 0;    foreach (dchar c; s) { // not nothrow        dstr[i] = c;        i++;    }    dstr = dstr[0 .. i];     foreach (j; 0 .. dstr.length / 2)        if (dstr[j] != dstr[\$ - j - 1])            return false;    return true;} void main() {    alias isPalindrome3 pali;    assert(pali(""));    assert(pali("z"));    assert(pali("aha"));    assert(pali("sees"));    assert(!pali("oofoe"));    assert(pali("deified"));    assert(!pali("Deified"));    assert(pali("amanaplanacanalpanama"));    assert(pali("ingirumimusnocteetconsumimurigni"));    assert(pali("salÃ las"));}`

### Low-level ASCII Version

`bool isPalindrome4(in string str) pure nothrow {    if (str.length == 0) return true;    immutable(char)* s = str.ptr;    immutable(char)* t = &(str[\$ - 1]);    while (s < t)        if (*s++ != *t--) // ugly            return false;    return true;} void main() {    alias isPalindrome4 pali;    assert(pali(""));    assert(pali("z"));    assert(pali("aha"));    assert(pali("sees"));    assert(!pali("oofoe"));    assert(pali("deified"));    assert(!pali("Deified"));    assert(pali("amanaplanacanalpanama"));    assert(pali("ingirumimusnocteetconsumimurigni"));    //assert(pali("salÃ las"));}`

## Dart

` bool isPalindrome(String s){    for(int i = 0; i < s.length/2;i++){    if(s[i] != s[(s.length-1) -i])      return false;          }    return true;  } `

## Delphi

`uses  SysUtils, StrUtils; function IsPalindrome(const aSrcString: string): Boolean;begin  Result := SameText(aSrcString, ReverseString(aSrcString));end;`

## Dyalect

`func isPalindrom(str) {    str == str.Reverse()} print(isPalindrom("ingirumimusnocteetconsumimurigni"))`

## Déjà Vu

`palindrome?:	local :seq chars	local :len-seq -- len seq 	for i range 0 / len-seq 2:		if /= seq! i seq! - len-seq i:			return false	true !. palindrome? "ingirumimusnocteetconsumimurigni"!. palindrome? "nope"`
Output:
```true
false```

## E

It is only necessarily to scan the first half of the string, `upper(0, upper.size() // 2)`, and compare each character to the corresponding character from the other end, `upper[last - i]`.

The for loop syntax is `for key pattern => value pattern in collection { ... }`, `?` imposes an additional boolean condition on a pattern (it may be read “such that”), and if the pattern does not match in a for loop then the iteration is skipped, so false is returned only if `upper[last - i] != c`.

`def isPalindrome(string :String) {  def upper := string.toUpperCase()  def last := upper.size() - 1  for i => c ? (upper[last - i] != c) in upper(0, upper.size() // 2) {     return false  }  return true}`

## EchoLisp

` ;; returns #t or #f(define (palindrome? string)(equal? (string->list string) (reverse (string->list string)))) ;; to strip spaces, use the following;;(define (palindrome? string);;(let ((string (string-replace string "/\ /" "" "g")));;(equal? (string->list string) (reverse (string->list string))))) `

## Eiffel

` 	is_palindrome (a_string: STRING): BOOLEAN			-- Is `a_string' a palindrome?		require			string_attached: a_string /= Void		local			l_index, l_count: INTEGER		do			from				Result := True				l_index := 1				l_count := a_string.count			until				l_index >= l_count - l_index + 1 or not Result			loop				Result := (Result and a_string [l_index] = a_string [l_count - l_index + 1])				l_index := l_index + 1			end		end `

## Ela

`open list string isPalindrome xs = xs == reverse xsisPalindrome <| toList "ingirumimusnocteetconsumimurigni" `

Function `reverse` is taken from list module and is defined as:

`reverse = foldl (flip (::)) (nil xs) foldl f z (x::xs) = foldl f (f z x) xsfoldl _ z []      = z `

## Elixir

` defmodule PalindromeDetection do  def is_palindrome(str), do: str == String.reverse(str)end `

Note: Because of Elixir's strong Unicode support, this even supports graphemes:

```iex(1)> PalindromeDetection.is_palindrome("salàlas")
true
iex(2)> PalindromeDetection.is_palindrome("as⃝df̅")
false
iex(3)> PalindromeDetection.is_palindrome("as⃝df̅f̅ds⃝a")
true
```

## Elm

`import String exposing (reverse, length) import Html exposing (Html, Attribute, text, div, input)import Html.Attributes exposing (placeholder, value, style)import Html.Events exposing (on, targetValue)import Html.App exposing (beginnerProgram) -- The following function (copied from Haskell) satisfies the -- rosettacode task description.is_palindrome x = x == reverse x -- The remainder of the code demonstrates the use of the function -- in a complete Elm program.main = beginnerProgram { model = "" , view = view , update = update } update newStr oldStr = newStr view : String -> Html Stringview candidate =  div []    ([ input        [ placeholder "Enter a string to check."        , value candidate        , on "input" targetValue         , myStyle        ]        []     ] ++      [ let testResult =              is_palindrome candidate            statement =              if testResult then "PALINDROME!" else "not a palindrome"        in div [ myStyle] [text statement]     ]) myStyle : Attribute msgmyStyle =  style    [ ("width", "100%")    , ("height", "20px")    , ("padding", "5px 0 0 5px")    , ("font-size", "1em")    , ("text-align", "left")    ]`

## Emacs Lisp

`(defun palindrome (s)  (string= s (reverse s)))`

## Erlang

` -module( palindrome ). -export( [is_palindrome/1, task/0] ). is_palindrome( String ) -> String =:= lists:reverse(String). task() ->	display( "abcba" ),	display( "abcdef" ),	Latin = "In girum imus nocte et consumimur igni",	No_spaces_same_case = lists:append( string:tokens(string:to_lower(Latin), " ") ),	display( Latin, No_spaces_same_case ).   display( String ) -> io:fwrite( "Is ~p a palindrom? ~p~n", [String, is_palindrome(String)] ). display( String1, String2 ) -> io:fwrite( "Is ~p a palindrom? ~p~n", [String1, is_palindrome(String2)] ). `
Output:
```22> palindrome:task().
Is "abcba" a palindrom? true
Is "abcdef" a palindrom? false
Is "In girum imus nocte et consumimur igni" a Latin palindrom? true
```

## Euphoria

`function isPalindrome(sequence s)    for i = 1 to length(s)/2 do        if s[i] != s[\$-i+1] then            return 0        end if    end for    return 1end function`
` include std/sequence.e -- reverseinclude std/console.e -- displayinclude std/text.e  -- upperinclude std/utils.e -- iif IsPalindrome("abcba")IsPalindrome("abcdef")IsPalindrome("In girum imus nocte et consumimur igni") procedure IsPalindrome(object s) display("Is '[]' a palindrome? ",{s},0) s = remove_all(' ',upper(s)) display(iif(equal(s,reverse(s)),"true","false"))end procedure`
Output:
```Is 'abcba' a palindrome? true
Is 'abcdef' a palindrome? false
Is 'In girum imus nocte et consumimur igni' a palindrome? true
```

## Excel

### LAMBDA

Binding the following lambda expression to the name ISPALINDROME in the Name Manager for the Excel WorkBook:

`ISPALINDROME=LAMBDA(s,    LET(        lcs, FILTERP(            LAMBDA(c, " " <> c)        )(            CHARS(LOWER(s))        ),        CONCAT(lcs) = CONCAT(REVERSE(lcs))    ))`

and assuming that the following generic lambdas are also bound to the names CHARS, FILTERP, and REVERSE in the Name Manager for the active WorkBook:

`CHARS=LAMBDA(s,    MID(s, ROW(INDIRECT("1:" & LEN(s))), 1))  FILTERP=LAMBDA(p,    LAMBDA(xs,        FILTER(xs, p(xs))    ))  REVERSE=LAMBDA(xs,    LET(        n, ROWS(xs),        SORTBY(            xs,            SEQUENCE(n, 1, n, -1)        )    ))`
Output:
 =ISPALINDROME(A2) fx A B 1 Test string Is palindrome ? 2 In girum imus nocte et consumimur igni TRUE 3 abban FALSE 4 abba TRUE 5 aba TRUE 6 ab FALSE 7 a TRUE

## F#

`let isPalindrome (s: string) =   let arr = s.ToCharArray()   arr = Array.rev arr`

Examples:

`isPalindrome "abcba"val it : bool = trueisPalindrome ("In girum imus nocte et consumimur igni".Replace(" ", "").ToLower());;val it : bool = trueisPalindrome "abcdef"val it : bool = false`

## Factor

`USING: kernel sequences ;: palindrome? ( str -- ? ) dup reverse = ;`

## Falcon

VBA/Python programmer's approach not sure if it's the most falconic way

` /* created by Aykayayciti Earl Lamont MontgomeryApril 9th, 2018 */ function is_palindrome(a)	a = strUpper(a).replace(" ", "")	b = a[-1:0]	return b == aend a = "mom"> is_palindrome(a) `
Output:
```true
[Finished in 1.7s]
```

more falconic

` /* created by Aykayayciti Earl Lamont MontgomeryApril 9th, 2018 */ b = "mom"> strUpper(b).replace(" ", "") == strUpper(b[-1:0]) ? "Is a palindrome" : "Is not a palindrome" `
Output:
```Is a palindrome
[Finished in 1.5s]
```

## Fantom

` class Palindrome{  // Function to test if given string is a palindrome  public static Bool isPalindrome (Str str)   {    str == str.reverse  }   // Give it a test run  public static Void main ()  {    echo (isPalindrome(""))    echo (isPalindrome("a"))    echo (isPalindrome("aa"))    echo (isPalindrome("aba"))    echo (isPalindrome("abb"))    echo (isPalindrome("salàlas"))    echo (isPalindrome("In girum imus nocte et consumimur igni".lower.replace(" ","")))  }} `

## FBSL

`#APPTYPE CONSOLE FUNCTION stripNonAlpha(BYVAL s AS STRING) AS STRING	DIM sTemp AS STRING = ""	DIM c AS STRING	FOR DIM i = 1 TO LEN(s)		c = MID(s, i, 1)		IF INSTR("ABCDEFGHIJKLMNOPQRSTUVWXYZ", c, 0, 1) THEN			sTemp = stemp & c		END IF	NEXT	RETURN sTempEND FUNCTION FUNCTION IsPalindrome(BYVAL s AS STRING) AS INTEGER	FOR DIM i = 1 TO STRLEN(s) \ 2 ' only check half of the string, as scanning from both ends		IF s{i} <> s{STRLEN - (i - 1)} THEN RETURN FALSE 'comparison is not case sensitive	NEXT 	RETURN TRUEEND FUNCTION PRINT IsPalindrome(stripNonAlpha("A Toyota"))PRINT IsPalindrome(stripNonAlpha("Madam, I'm Adam"))PRINT IsPalindrome(stripNonAlpha("the rain in Spain falls mainly on the rooftops")) PAUSE `
Output:
``` 1
1
0
```

## Forth

`: first   over [email protected] ;: last    >r 2dup + 1- [email protected] r> swap ;: palindrome? ( c-addr u -- f )  begin    dup 1 <=      if 2drop true  exit then    first last <> if 2drop false exit then    1 /string 1-  again ; `

FIRST and LAST are once-off words that could be beheaded immediately afterwards. The version taking advantage of Tail Call Optimization or a properly tail-recursive variant of RECURSE (easily added to any Forth) is very similar. The horizontal formatting highlights the parallel code - and potential factor; a library of many string tests like this could have ?SUCCESS and ?FAIL .

Below is a separate Forth program that detects palindrome phrases as well as single word palindromes. It was programmed using gforth.

` variable temp-addr : valid-char? ( addr1 u -- f ) ( check for valid character )    + dup [email protected] 48 58 within    over [email protected] 65 91 within or    swap [email protected] 97 123 within or ; : >upper ( c1 -- c2 )    dup 97 123 within if 32 - then ; : strip-input ( addr1 u -- addr2 u ) ( Strip characters, then copy stripped string to temp-addr )    pad temp-addr !    temp-addr @ rot rot 0 do dup I 2dup valid-char? if        + [email protected] >upper temp-addr @ C! 1 temp-addr +!        else 2drop        then loop drop temp-addr @ pad - ; : get-phrase ( -- addr1 u )    ." Type a phrase: " here 1024 accept here swap -trailing cr ; : position-phrase ( addr1 u -- addr1 u addr2 u addr1 addr2 u )    temp-addr @ over 2over 2over drop swap ; : reverse-copy ( addr1 addr2 u -- addr1 addr2 )    0 do over I' 1- I - + over I + 1 cmove loop 2drop ; : palindrome? ( -- )    get-phrase strip-input position-phrase reverse-copy compare 0= if    ." << Valid >> Palindrome."    else ." << Not >> a Palindrome."    then cr ; `

Example:

palindrome?
Type a phrase: A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal-Panama!

<< Valid >> Palindrome.

## Fortran

Works with: Fortran version 90 and later
`program palindro   implicit none   character(len=*), parameter :: p = "ingirumimusnocteetconsumimurigni"   print *, is_palindro_r(p)  print *, is_palindro_r("anothertest")  print *, is_palindro2(p)  print *, is_palindro2("test")  print *, is_palindro(p)  print *, is_palindro("last test") contains`

Non-recursive

`! non-recursivefunction is_palindro(t)  logical :: is_palindro  character(len=*), intent(in) :: t   integer :: i, l   l = len(t)  is_palindro = .false.  do i=1, l/2     if ( t(i:i) /= t(l-i+1:l-i+1) ) return  end do  is_palindro = .true.end function is_palindro ! non-recursive 2function is_palindro2(t) result(isp)  logical :: isp  character(len=*), intent(in) :: t   character(len=len(t)) :: s  integer :: i   forall(i=1:len(t)) s(len(t)-i+1:len(t)-i+1) = t(i:i)  isp = ( s == t )end function is_palindro2`

Recursive

`  recursive function is_palindro_r (t) result (isp)     implicit none    character (*), intent (in) :: t    logical :: isp     isp = len (t) == 0 .or. t (: 1) == t (len (t) :) .and. is_palindro_r (t (2 : len (t) - 1))   end function is_palindro_r`
`end program palindro`

## FreeBASIC

`' version 20-06-2015' compile with: fbc -s console "filename".bas #Ifndef TRUE        ' define true and false for older freebasic versions    #Define FALSE 0    #Define TRUE Not FALSE#EndIf Function reverse(norm As String) As Integer     Dim As String rev    Dim As Integer i, l = Len(norm) -1     rev = norm    For i = 0 To l        rev[l-i] = norm[i]    Next     If norm = rev Then        Return TRUE    Else        Return FALSE    End If End Function Function cleanup(in As String, action As String = "") As String    ' action = "" do nothing, [l|L] = convert to lowercase,    ' [s|S] = strip spaces,  [p|P] = strip punctuation.    If action = "" Then Return in     Dim As Integer i, p_, s_    Dim As String ch     action = LCase(action)    For i = 1 To Len(action)        ch = Mid(action, i, 1)        If ch = "l" Then in = LCase(in)        If ch = "p" Then            p_ = 1        ElseIf ch = "s" Then            s_ = 1        End If    Next     If p_ = 0 And s_ = 0 Then Return in     Dim As String unwanted, clean     If s_ = 1 Then unwanted = " "    If p_ = 1 Then unwanted = unwanted + "`[email protected]#\$%^&*()-=_+[]{}\|;:',.<>/?"     For i = 1 To Len(in)        ch = Mid(in, i, 1)        If InStr(unwanted, ch) = 0 Then clean = clean + ch    Next     Return clean End Function ' ------=< MAIN >=------ Dim As String test = "In girum imus nocte et consumimur igni"'IIf ( cond, true, false ), true and false must be of the same type (num, string, UDT)PrintPrint "                 reverse(test) = "; IIf(reverse(test) = FALSE, "FALSE", "TRUE")Print "  reverse(cleanup(test,""l"")) = "; IIf(reverse(cleanup(test,"l")) = FALSE, "FALSE", "TRUE")Print " reverse(cleanup(test,""ls"")) = "; IIf(reverse(cleanup(test,"ls")) = FALSE, "FALSE", "TRUE")Print "reverse(cleanup(test,""PLS"")) = "; IIf(reverse(cleanup(test,"PLS")) = FALSE, "FALSE", "TRUE") ' empty keyboard bufferWhile InKey <> "" : WendPrint : Print : Print "Hit any key to end program"SleepEnd`
Output:
```               reverse(test) = FALSE
reverse(cleanup(test,"l")) = FALSE
reverse(cleanup(test,"ls")) = TRUE
reverse(cleanup(test,"PLS")) = TRUE```

## Frink

This version will even work with upper-plane Unicode characters. Many languages will not work correctly with upper-plane Unicode characters because they are represented as Unicode "surrogate pairs" which are represented as two characters in a UTF-16 stream. In addition, Frink uses a grapheme-based reverse, which allows the algorithm below to operate on combined sequences of Unicode characters.

For example, the string "og\u0308o" represents an o, a g with combining diaeresis, followed by the letter o. Or, in other words, "og̈o". Note that while there are four Unicode codepoints, only three "graphemes" are displayed. Using Frink's smart "reverse" function preserves these combined graphemes and detects them correctly as palindromes.

`isPalindrome[x] := x == reverse[x] `

Test in Frink with upper-plane Unicode:

`isPalindrome["x\u{1f638}x"]`

``` true ```

## Fōrmulæ

Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text. Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for storage and transfer purposes more than visualization and edition.

Programs in Fōrmulæ are created/edited online in its website, However they run on execution servers. By default remote servers are used, but they are limited in memory and processing power, since they are intended for demonstration and casual use. A local server can be downloaded and installed, it has no limitations (it runs in your own computer). Because of that, example programs can be fully visualized and edited, but some of them will not run if they require a moderate or heavy computation/memory resources, and no local server is being used.

## GAP

`ZapGremlins := function(s)  local upper, lower, c, i, n, t;  upper := "ABCDEFGHIJKLMNOPQRSTUVWXYZ";  lower := "abcdefghijklmnopqrstuvwxyz";  t := [ ];  i := 1;  for c in s do    n := Position(upper, c);    if n <> fail then      t[i] := lower[n];      i := i + 1;    else      n := Position(lower, c);      if n <> fail then        t[i] := c;        i := i + 1;      fi;    fi;  od;  return t;end; IsPalindrome := function(s)  local t;  t := ZapGremlins(s);  return t = Reversed(t);end;`

## GML

` //Setting a var from an argument passed to the scriptvar str;str = argument0//Takes out all spaces/anything that is not a letter or a number and turns uppercase letters to lowercasestr = string_lettersdigits(string_lower(string_replace(str,' ','')));var inv;inv = '';//for loop that reverses the sequencevar i;for (i = 0; i < string_length(str); i += 1;)    {    inv += string_copy(str,string_length(str)-i,1);    }//returns true if the sequence is a palindrome else returns falsereturn (str == inv); `

Palindrome detection using a Downward For-Loop

`  //Remove everything except for letters and digits and convert the string to lowercase. source is what will be compared to str.var str = string_lower(string_lettersdigits(string_replace(argument0," ",""))), source = ""; //Loop through and store each character of str in source.for (var i = string_length(str); i > 0; i--) {    source += string_char_at(str,i);} //Return if it is a palindrome.return source == str; `

## Go

`package pal func IsPal(s string) bool {    mid := len(s) / 2    last := len(s) - 1    for i := 0; i < mid; i++ {        if s[i] != s[last-i] {            return false        }    }    return true}`

This version works with Unicode,

` func isPalindrome(s string) bool {	runes := []rune(s)	numRunes := len(runes) - 1	for i := 0; i < len(runes)/2; i++ {		if runes[i] != runes[numRunes-i] {			return false		}	}	return true}`

Or using more slicing,

` func isPalindrome(s string) bool {	runes := []rune(s)	for len(runes) > 1 {		if runes[0] != runes[len(runes)-1] {			return false		}		runes = runes[1 : len(runes)-1]	}	return true}`

## Groovy

### Trivial

Solution:

`def isPalindrome = { String s ->    s == s?.reverse()}`

Test program:

`println isPalindrome("")println isPalindrome("a")println isPalindrome("abcdefgfedcba")println isPalindrome("abcdeffedcba")println isPalindrome("abcedfgfedcb")`
Output:
```true
true
true
true
false```

This solution assumes nulls are palindromes.

### Non-recursive

Solution:

`def isPalindrome = { String s ->    def n = s.size()    n < 2 || s[0..<n/2] == s[-1..(-n/2)]}`

Test program and output are the same. This solution does not handle nulls.

### Recursive

Solution follows the C palindrome_r recursive solution:

`def isPalindromeisPalindrome = { String s ->    def n = s.size()    n < 2 || (s[0] == s[n-1] && isPalindrome(s[1..<(n-1)]))}`

Test program and output are the same. This solution does not handle nulls.

Non-recursive

A string is a palindrome if reversing it we obtain the same string.

`is_palindrome x = x == reverse x`

Or, applicative and point-free, with some pre-processing of data (shedding white space and upper case):

`import Data.Bifunctor (second)import Data.Char (toLower) ------------------- PALINDROME DETECTION ----------------- isPalindrome :: Eq a => [a] -> BoolisPalindrome = (==) <*> reverse -- Or, comparing just the leftward characters with-- with a reflection of just the rightward characters. isPal :: String -> BoolisPal s =  let (q, r) = quotRem (length s) 2   in uncurry (==) \$        second (reverse . drop r) \$ splitAt q s --------------------------- TEST -------------------------main :: IO ()main =  mapM_ putStrLn \$    (showResult <\$> [isPalindrome, isPal])      <*> fmap        prepared        [ "",          "a",          "ab",          "aba",          "abba",          "In girum imus nocte et consumimur igni"        ] prepared :: String -> Stringprepared cs = [toLower c | c <- cs, ' ' /= c] showResult f s = (show s) <> " -> " <> show (f s)`
Output:
```"" -> True
"a" -> True
"ab" -> False
"aba" -> True
"abba" -> True
"ingirumimusnocteetconsumimurigni" -> True
"" -> True
"a" -> True
"ab" -> False
"aba" -> True
"abba" -> True
"ingirumimusnocteetconsumimurigni" -> True```

Recursive

See the C palindrome_r code for an explanation of the concept used in this solution, though it may be better suited to indexed arrays than to linked lists.

(last is expensive, and entails multiplied recursions over the right hand side of the remaining list here).

`is_palindrome_r x | length x <= 1 = True                  | head x == last x = is_palindrome_r . tail. init \$ x                  | otherwise = False`

## HicEst

 This example is incorrect. Please fix the code and remove this message.Details: The stripping of spaces and case conversion should be outside the palindrome detection.
`   result = Palindrome( "In girum imus nocte et consumimur igni" ) ! returns 1END FUNCTION Palindrome(string)   CHARACTER string, CopyOfString    L = LEN(string)   ALLOCATE(CopyOfString, L)   CopyOfString = string   EDIT(Text=CopyOfString, UpperCase=L)   L = L - EDIT(Text=CopyOfString, End, Left=' ', Delete, DO=L) ! EDIT returns number of deleted spaces    DO i = 1, L/2     Palindrome = CopyOfString(i) == CopyOfString(L - i + 1)     IF( Palindrome == 0 ) RETURN   ENDDOEND`

## Icon and Unicon

`procedure main(arglist)every writes(s := !arglist) do write( if palindrome(s) then " is " else " is not", " a palindrome.")end`

The following simple procedure uses the built-in reverse. Reverse creates a transient string which will get garbage collected.

`procedure palindrome(s)  #: return s if s is a palindromereturn s == reverse(s)end`

Note: The IPL procedure strings contains a palindrome tester called ispal that uses reverse and is equivalent to the version of palindrome above.

This version uses positive and negative sub-scripting and works not only on strings but lists of strings, such as ["ab","ab"] or ["ab","x"] the first list would pass the test but the second wouldn't.

`procedure palindrome(x)  #: return x if s is x palindromelocal ievery if x[i := 1 to (*x+ 1)/2] ~== x[-i] then failreturn xend`

## Ioke

`Text isPalindrome? = method(self chars == self chars reverse)`

## J

Non-recursive

Reverse and match method

`isPalin0=: -: |.`

Example usage

`   isPalin0 'ABBA'1   isPalin0 -.&' ' tolower 'In girum imus nocte et consumimur igni'1`

Recursive

Tacit and explicit verbs:

`isPalin1=: 0:`(\$:@(}[email protected]}:))@.({.={:)`1:@.(1>:#) isPalin2=: monad define if. 1>:#y do. 1 return. end. if. ({.={:)y do. isPalin2 }.}:y else. 0 end.)`

Note that while these recursive verbs are bulkier and more complicated, they are also several thousand times more inefficient than isPalin0.

`   foo=: foo,|.foo=:2000\$a.   ts=:6!:2,7!:2  NB. time and space required to execute sentence   ts 'isPalin0 foo'2.73778e_5 5184   ts 'isPalin1 foo'0.0306667 6.0368e6   ts 'isPalin2 foo'0.104391 1.37965e7   'isPalin1 foo' %&ts 'isPalin0 foo'1599.09 1164.23   'isPalin2 foo' %&ts 'isPalin0 foo'3967.53 2627.04`

## Java

Non-Recursive

`public static boolean pali(String testMe){	StringBuilder sb = new StringBuilder(testMe);	return testMe.equals(sb.reverse().toString());}`

Non-Recursive using indexes (supports upper-plane Unicode)

`public static boolean isPalindrome(String input) {	for (int i = 0, j = input.length() - 1; i < j; i++, j--) {		char startChar = input.charAt(i);		char endChar = input.charAt(j); 		// Handle surrogate pairs in UTF-16		if (Character.isLowSurrogate(endChar)) {			if (startChar != input.charAt(--j)) {				return false;			}			if (input.charAt(++i) != endChar) {				return false;			}		} else if (startChar != endChar) {			return false;		}	}	return true;}`

Recursive (this version does not work correctly with upper-plane Unicode)

`public static boolean rPali(String testMe){	if(testMe.length()<=1){		return true;	}	if(!(testMe.charAt(0)+"").equals(testMe.charAt(testMe.length()-1)+"")){		return false;	}	return rPali(testMe.substring(1, testMe.length()-1));}`

Recursive using indexes (this version does not work correctly with upper-plane Unicode)

`public static boolean rPali(String testMe){	int strLen = testMe.length();	return rPaliHelp(testMe, strLen-1, strLen/2, 0);} public static boolean rPaliHelp(String testMe, int strLen, int testLen, int index){	if(index > testLen){		return true;	}	if(testMe.charAt(index) != testMe.charAt(strLen-index)){		return false;	}	return rPaliHelp(testMe, strLen, testLen, index + 1);} `

Regular Expression (source)

`public static boolean pali(String testMe){	return testMe.matches("|(?:(.)(?<=(?=^.*?(\\1\\2?)\$).*))+(?<=(?=^\\2\$).*)");}`

## JavaScript

`function isPalindrome(str) {  return str === str.split("").reverse().join("");} console.log(isPalindrome("ingirumimusnocteetconsumimurigni"));`

ES6 implementation

`var isPal = str => str === str.split("").reverse().join("");`

Or, ignoring spaces and variations in case:

`(() => {     // isPalindrome :: String -> Bool    const isPalindrome = s => {        const cs = filter(c => ' ' !== c, s.toLocaleLowerCase());        return cs.join('') === reverse(cs).join('');    };      // TEST -----------------------------------------------    const main = () =>        isPalindrome(            'In girum imus nocte et consumimur igni'        )     // GENERIC FUNCTIONS ----------------------------------     // filter :: (a -> Bool) -> [a] -> [a]    const filter = (f, xs) => (        'string' !== typeof xs ? (            xs        ) : xs.split('')    ).filter(f);     // reverse :: [a] -> [a]    const reverse = xs =>        'string' !== typeof xs ? (            xs.slice(0).reverse()        ) : xs.split('').reverse().join('');     // MAIN ---    return main();})();`
Output:
`true`

## jq

`def palindrome: explode as \$in | (\$in|reverse) == \$in;`

Example:

```"salàlas" | palindrome
```
Output:
```true
```

## Jsish

`/* Palindrome detection, in Jsish */function isPalindrome(str:string, exact:boolean=true) {  if (!exact) {      str = str.toLowerCase();      str = str.replace(/[ \t,;:!?.]/g, '');  }  return str === str.match(/./g).reverse().join('');} ;isPalindrome('BUB');;isPalindrome('CUB');;isPalindrome('Bub');;isPalindrome('Bub', false);;isPalindrome('In girum imus nocte et consumimur igni', false);;isPalindrome('A man, a plan, a canal; Panama!', false);;isPalindrome('Never odd or even', false); /*=!EXPECTSTART!=isPalindrome('BUB') ==> trueisPalindrome('CUB') ==> falseisPalindrome('Bub') ==> falseisPalindrome('Bub', false) ==> trueisPalindrome('In girum imus nocte et consumimur igni', false) ==> trueisPalindrome('A man, a plan, a canal; Panama!', false) ==> trueisPalindrome('Never odd or even', false) ==> true=!EXPECTEND!=*/`

Most of that code is for testing, using echo mode lines (semicolon in column 1)

Output:
```prompt\$ jsish --U palindrome.jsi
isPalindrome('BUB') ==> true
isPalindrome('CUB') ==> false
isPalindrome('Bub') ==> false
isPalindrome('Bub', false) ==> true
isPalindrome('In girum imus nocte et consumimur igni', false) ==> true
isPalindrome('A man, a plan, a canal; Panama!', false) ==> true
isPalindrome('Never odd or even', false) ==> true

prompt\$ jsish -u palindrome.jsi
[PASS] palindrome.jsi```

## Julia

`palindrome(s) = s == reverse(s)`

Non-Recursive

` function palindrome(s)    len = length(s)    for i = 1:(len/2)        if(s[len-i+1]!=s[i])            return false        end    end    return trueend `

Recursive

` function palindrome(s)    len = length(s)    if(len==0 || len==1)        return true    end    if(s[1] == s[len])        return palindrome(SubString(s,2,len-1))    end    return falseend`

## k

`is_palindrome:{x~|x}`

## Kotlin

`// version 1.1.2 /* These functions deal automatically with Unicode as all strings are UTF-16 encoded in Kotlin */ fun isExactPalindrome(s: String) = (s == s.reversed()) fun isInexactPalindrome(s: String): Boolean {    var t = ""    for (c in s) if (c.isLetterOrDigit()) t += c    t = t.toLowerCase()    return t == t.reversed()} fun main(args: Array<String>) {    val candidates = arrayOf("rotor", "rosetta", "step on no pets", "été")    for (candidate in candidates) {        println("'\$candidate' is \${if (isExactPalindrome(candidate)) "an" else "not an"} exact palindrome")    }    println()    val candidates2 = arrayOf(         "In girum imus nocte et consumimur igni",         "Rise to vote, sir",         "A man, a plan, a canal - Panama!",         "Ce repère, Perec"  // note: 'è' considered a distinct character from 'e'    )    for (candidate in candidates2) {        println("'\$candidate' is \${if (isInexactPalindrome(candidate)) "an" else "not an"} inexact palindrome")    }}`
Output:
```'rotor' is an exact palindrome
'rosetta' is not an exact palindrome
'step on no pets' is an exact palindrome
'été' is an exact palindrome

'In girum imus nocte et consumimur igni' is an inexact palindrome
'Rise to vote, sir' is an inexact palindrome
'A man, a plan, a canal - Panama!' is an inexact palindrome
'Ce repère, Perec' is not an inexact palindrome
```

## LabVIEW

This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.

## langur

`val .ispal = f len(.s) > 0 and .s == s2s .s, len(.s)..1 val .tests = h{    "": false,    "z": true,    "aha": true,    "αηα": true,    "αννα": true,    "αννασ": false,    "sees": true,    "seas": false,    "deified": true,    "solo": false,    "solos": true,    "amanaplanacanalpanama": true,    "a man a plan a canal panama": false,   # true if we remove spaces    "ingirumimusnocteetconsumimurigni": true,} for .word in sort(keys .tests) {    val .foundpal = .ispal(.word)    writeln .word, ": ", .foundpal, if(.foundpal == .tests[.word]: ""; " (FAILED TEST)")}`
Output:
```: false
a man a plan a canal panama: false
aha: true
amanaplanacanalpanama: true
deified: true
ingirumimusnocteetconsumimurigni: true
seas: false
sees: true
solo: false
solos: true
z: true
αηα: true
αννα: true
αννασ: false```

## Lasso

`define ispalindrome(text::string) => { 	local(_text = string(#text)) // need to make copy to get rid of reference issues 	#_text -> replace(regexp(`(?:\$|\W)+`), -ignorecase) 	local(reversed = string(#_text))	#reversed -> reverse 	return #_text == #reversed} ispalindrome('Tätatät') // works with high asciiispalindrome('Hello World') ispalindrome('A man, a plan, a canoe, pasta, heros, rajahs, a coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal – Panama!')`
Output:
```true
false
true```

## Liberty BASIC

`print isPalindrome("In girum imus nocte et consumimur igni")print isPalindrome(removePunctuation\$("In girum imus nocte et consumimur igni", "S"))print isPalindrome(removePunctuation\$("In girum imus nocte et consumimur igni", "SC")) function isPalindrome(string\$)    isPalindrome = 1    for i = 1 to int(len(string\$)/2)        if mid\$(string\$, i, 1) <> mid\$(string\$, len(string\$)-i+1, 1) then isPalindrome = 0 : exit function    next iend function function removePunctuation\$(string\$, remove\$)    'P = remove puctuation.  S = remove spaces   C = remove case    If instr(upper\$(remove\$), "C") then string\$ = lower\$(string\$)    If instr(upper\$(remove\$), "P") then removeCharacters\$ = ",.!'()-&*?<>:;~[]{}"    If instr(upper\$(remove\$), "S") then removeCharacters\$ = removeCharacters\$;" "     for i = 1 to len(string\$)        if instr(removeCharacters\$, mid\$(string\$, i, 1)) then string\$ = left\$(string\$, i-1);right\$(string\$, len(string\$)-i) : i = i - 1    next i    removePunctuation\$ = string\$end function`
Output:
```0
0
1
```

## LiveCode

This implementation defaults to exact match, but has an optional parameter to do inexact.
`function palindrome txt exact    if exact is empty or exact is not false then         set caseSensitive to true  --default is false    else        replace space with empty in txt        put lower(txt) into txt    end if    return txt is reverse(txt) end palindrome function reverse str    repeat with i = the length of str down to 1        put byte i of str after revstr    end repeat    return revstrend reverse`

## Logo

`to palindrome? :w  output equal? :w reverse :wend`

## Lua

`function ispalindrome(s) return s == string.reverse(s) end`

## M4

Non-recursive This uses the `invert` from Reversing a string.

`define(`palindrorev',`ifelse(`\$1',invert(`\$1'),`yes',`no')')dnlpalindrorev(`ingirumimusnocteetconsumimurigni')palindrorev(`this is not palindrome')`

Recursive

`define(`striptwo',`substr(`\$1',1,eval(len(`\$1')-2))')dnldefine(`cmplast',`ifelse(`striptwo(`\$1')',,`yes',dnlsubstr(`\$1',0,1),substr(`\$1',eval(len(`\$1')-1),1),`yes',`no')')dnldefine(`palindro',`dnlifelse(eval(len(`\$1')<1),1,`yes',cmplast(`\$1'),`yes',`palindro(striptwo(`\$1'))',`no')')dnlpalindro(`ingirumimusnocteetconsumimurigni')palindro(`this is not palindrome')`

## Maple

This uses functions from Maple's built-in `StringTools` package.

` with(StringTools): IsPalindrome("ingirumimusnocteetconsumimurigni"); IsPalindrome("In girum imus nocte et consumimur igni"); IsPalindrome(LowerCase(DeleteSpace("In girum imus nocte et consumimur igni"))); `
Output:
```                                    true

false

true
```

## Mathematica/Wolfram Language

Built-in function handling lists, numbers, and strings:

`PalindromeQ`
Examples:
```PalindromeQ["TNT"]
PalindromeQ["test"]
PalindromeQ["deified"]
PalindromeQ["salálas"]
PalindromeQ["ingirumimusnocteetconsumimurigni"]```
Output:
```True
False
True
True
True```

## MATLAB

`function trueFalse = isPalindrome(string)     trueFalse = all(string == fliplr(string)); %See if flipping the string produces the original string     if not(trueFalse) %If not a palindrome        string = lower(string); %Lower case everything        trueFalse = all(string == fliplr(string)); %Test again    end     if not(trueFalse) %If still not a palindrome        string(isspace(string)) = []; %Strip all space characters out        trueFalse = all(string == fliplr(string)); %Test one last time    end end`
Sample Usage:
`>> isPalindrome('In girum imus nocte et consumimur igni') ans =      1 `

## Maxima

`palindromep(s) := block([t], t: sremove(" ", sdowncase(s)), sequal(t, sreverse(t)))\$ palindromep("Sator arepo tenet opera rotas");  /* true */`

## MAXScript

Non-recursive

`fn isPalindrome s =(    local reversed = ""    for i in s.count to 1 by -1 do reversed += s[i]    return reversed == s)`

Recursive

`fn isPalindrome_r s =(    if s.count <= 1 then    (        true    )    else    (        if s[1] != s[s.count] then        (            return false        )        isPalindrome_r (substring s 2 (s.count-2))    ))`

Testing

`local p = "ingirumimusnocteetconsumimurigni"format ("'%' is a palindrome? %\n") p (isPalindrome p)format ("'%' is a palindrome? %\n") p (isPalindrome_r p)`

## min

Works with: min version 0.19.3
`(dup reverse ==) :palindrome?(dup "" split reverse "" join ==) :str-palindrome? "apple" str-palindrome? puts"racecar" str-palindrome? puts(a b c) palindrome? puts(a b b a) palindrome? puts`
Output:
```false
true
false
true
```

## MiniScript

`isPalindrome = function(s)    // convert to lowercase, and strip non-letters    stripped = ""    for c in s.lower    	if c >= "a" and c <= "z" then stripped = stripped + c    end for     // check palindromity    mid = floor(stripped.len/2)    for i in range(0, mid)    	if stripped[i] != stripped[-i - 1] then return false    end for    return trueend function testStr = "Madam, I'm Adam"answer = [testStr, "is"]if not isPalindrome(testStr) then answer.push "NOT"answer.push "a palindrome"print answer.join`
Output:
```Madam, I'm Adam is a palindrome
```

## Mirah

`def reverse(s:string)     StringBuilder.new(s).reverse.toString()end def palindrome?(s:string)     s.equals(reverse(s))end puts palindrome?("anna")        # ==> trueputs palindrome?("Erik")        # ==> falseputs palindrome?("palindroom-moordnilap") # ==> trueputs nil                        # ==> null`

## ML

### mLite

`fun to_locase s = implode ` map (c_downcase) ` explode s fun only_alpha s = implode ` filter (fn x = c_alphabetic x) ` explode s fun is_palin	( h1 :: t1, h2 :: t2, n = 0 ) 		       = true|	( h1 :: t1, h2 :: t2, n ) where ( h1 eql h2 )  = is_palin( t1, t2, n - 1)|	( h1 :: t1, h2 :: t2, n )                      = false|       (str s) =		let			val es = explode ` to_locase ` only_alpha s;			val res = rev es;			val k = (len es) div 2		in			is_palin (es, res, k)		end fun test_is_palin s =	(print "\""; print s; print "\" is a palindrome: "; print ` is_palin s; println "") fun test (f, arg, res, ok, notok) = if (f arg eql res) then ("'" @ arg @ "' " @ ok) else ("'" @ arg @ "' " @ notok) ; println ` test (is_palin, "In girum imus nocte, et consumimur igni", true, "is a palindrome", "is NOT a palindrome");println ` test (is_palin, "Madam, I'm Adam.", true, "is a palindrome", "is NOT a palindrome");println ` test (is_palin, "salàlas", true, "is a palindrome", "is NOT a palindrome");println ` test (is_palin, "radar", true, "is a palindrome", "is NOT a palindrome");println ` test (is_palin, "Lagerregal", true, "is a palindrome", "is NOT a palindrome");println ` test (is_palin, "Ein Neger mit Gazelle zagt im Regen nie.", true, "is a palindrome", "is NOT a palindrome");println ` test (is_palin, "something wrong", true, "is a palindrome", "is NOT a palindrome");`

Output:

```'In girum imus nocte, et consumimur igni' is a palindrome
'salàlas' is a palindrome
'Lagerregal' is a palindrome
'Ein Neger mit Gazelle zagt im Regen nie.' is a palindrome
'something wrong' is NOT a palindrome
```

### Standard ML

` fun palindrome s =  let val cs = explode s in    cs = rev cs  end `

## MMIX

`argc     IS \$0argv     IS \$1          LOC Data_SegmentDataSeg  GREG @           LOC @+1000ItsPalStr IS @-Data_Segment          BYTE "It's palindrome",10,0          LOC @+(8-@)&7NoPalStr  IS  @-Data_Segment          BYTE "It is not palindrome",10,0          LOC #100         GREG @% input: \$255 points to where the string to be checked is% returns \$255 0 if not palindrome, not zero otherwise% trashs: \$0,\$1,\$2,\$3% return address \$4DetectPalindrome LOC @         ADDU \$1,\$255,0      % \$1 = \$2552H       LDB  \$0,\$1,0        % get byte at \$1         BZ   \$0,1F          % if zero, end (length)         INCL \$1,1           % \$1++         JMP  2B             % loop1H       SUBU \$1,\$1,1        % ptr last char of string         ADDU \$0,DataSeg,0   % \$0 to data seg.3H       CMP  \$3,\$1,\$255     % is \$0 == \$255?         BZ   \$3,4F          % then jump         LDB  \$3,\$1,0        % otherwise get the byte         STB  \$3,\$0,0        % and copy it         INCL \$0,1           % \$0++         SUB  \$1,\$1,1        % \$1--         JMP  3B4H       LDB  \$3,\$1,0         STB  \$3,\$0,0        % copy the last byte% now let us compare reversed string and straight string         XOR  \$0,\$0,\$0       % index         ADDU \$1,DataSeg,06H       LDB  \$2,\$1,\$0       % pick char from rev str         LDB  \$3,\$255,\$0     % pick char from straight str         BZ   \$3,PaliOk      % finished as palindrome         CMP  \$2,\$2,\$3       % == ?         BNZ  \$2,5F          % if not, exit         INCL \$0,1           % \$0++         JMP  6B5H       XOR  \$255,\$255,\$255         GO   \$4,\$4,0        % return falsePaliOk   NEG  \$255,0,1                GO   \$4,\$4,0        % return true% The Main for testing the function% run from the command line% \$ mmix ./palindrome.mmo ingirumimusnocteetconsumimurigniMain     CMP  argc,argc,2    % argc > 2?         BN   argc,3F        % no -> not enough arg         ADDU \$1,\$1,8        % argv+1         LDOU \$255,\$1,0      % argv[1]         GO   \$4,DetectPalindrome         BZ   \$255,2F        % if not palindrome, jmp         SETL \$0,ItsPalStr   % pal string         ADDU \$255,DataSeg,\$0         JMP  1F2H       SETL \$0,NoPalStr    % no pal string         ADDU \$255,DataSeg,\$01H       TRAP 0,Fputs,StdOut % print3H       XOR  \$255,\$255,\$255         TRAP 0,Halt,0       % exit(0)`

## Modula-2

`MODULE Palindrome;FROM FormatString IMPORT FormatString;FROM Terminal IMPORT WriteString,ReadChar; PROCEDURE IsPalindrome(str : ARRAY OF CHAR) : BOOLEAN;VAR i,m : INTEGER;VAR buf : ARRAY[0..63] OF CHAR;BEGIN    i := 0;    m := HIGH(str) - 1;    WHILE i<m DO        IF str[i] # str[m-i] THEN            RETURN FALSE        END;        INC(i)    END;    RETURN TRUEEND IsPalindrome; PROCEDURE Print(str : ARRAY OF CHAR);VAR buf : ARRAY[0..63] OF CHAR;BEGIN    FormatString("%s: %b\n", buf, str, IsPalindrome(str));    WriteString(buf)END Print; BEGIN    Print("");    Print("z");    Print("aha");    Print("sees");    Print("oofoe");    Print("deified");    Print("Deified");    Print("amanaplanacanalpanama");    Print("ingirumimusnocteetconsumimurigni");     ReadCharEND Palindrome.`

## Modula-3

`MODULE Palindrome; IMPORT Text; PROCEDURE isPalindrome(string: TEXT): BOOLEAN =  VAR len := Text.Length(string);  BEGIN    FOR i := 0 TO len DIV 2 - 1 DO      IF Text.GetChar(string, i) # Text.GetChar(string, (len - i - 1)) THEN        RETURN FALSE;      END;    END;    RETURN TRUE;  END isPalindrome;END Palindrome.`

## Nanoquery

`def is_palindrome(s)        temp = ""        for char in s                if "abcdefghikjklmnopqrstuvwxyz" .contains. lower(char)                        temp += lower(char)                end        end         return list(temp) = list(temp).reverse()end`

## Nemerle

`using System;using System.Console;using Nemerle.Utility.NString; //contains methods Explode() and Implode() which convert string -> list[char] and back module Palindrome{    IsPalindrome( text : string) : bool    {        Implode(Explode(text).Reverse()) == text;    }     Main() : void    {        WriteLine("radar is a palindrome: {0}", IsPalindrome("radar"));    }}`

And a function to remove spaces and punctuation and convert to lowercase

`Clean( text : string ) : string{    def sepchars = Explode(",.;:-?!()' ");    Concat( "", Split(text, sepchars)).ToLower()}`

## NetRexx

Translation of: REXX
` y='In girum imus nocte et consumimur igni' -- translation: We walk around in the night and-- we are burnt by the fire (of love)saysay 'string = 'ysay pal=isPal(y) if pal==0 then say "The string isn't palindromic."          else say 'The string is palindromic.' method isPal(x) static  x=x.upper().space(0)          /* removes all blanks (spaces)          */                                /*   and translate to uppercase.        */  return x==x.reverse()         /* returns  1  if exactly equal         */ `

## NewLISP

Works likewise for strings and for lists

` (define (palindrome? s)    (setq r s)    (reverse r) ; Reverse is destructive.    (= s r)) ;; Make ‘reverse’ non-destructive and avoid a global variable(define (palindrome? s)    (= s (reverse (copy s)))) `

## Nim

The following program detects if UTF-8 strings are exact palindromes. If "exact" is set to "false", it ignores the white spaces and the differences of letter case to detect inexact palindromes. Differences in punctuation are still relevant.

`import unicode  func isPalindrome(rseq: seq[Rune]): bool =  ## Return true if a sequence of runes is a palindrome.  for i in 1..(rseq.len shr 1):    if rseq[i - 1] != rseq[^i]:      return false  result = true  func isPalindrome(str: string; exact = true): bool {.inline.} =  ## Return true if a UTF-8 string is a palindrome.  ## If "exact" is false, ignore white spaces and ignore case.   if exact:    result = str.toRunes.isPalindrome()  else:    var rseq: seq[Rune]    for rune in str.runes:      if not rune.isWhiteSpace:        rseq.add rune.toLower    result = rseq.isPalindrome()  when isMainModule:   proc check(s: string) =    var exact, inexact: bool    exact = s.isPalindrome()    if not exact:      inexact = s.isPalindrome(exact = false)    let txt = if exact: " is an exact palindrome."              elif inexact: " is an inexact palindrome."              else: " is not a palindrome."    echo '"', s, '"', txt check "rotor"check "été"check "αννα"check "salÃ las"check "In girum imus nocte et consumimur igni"check "Esope reste ici et se repose"check "This is a palindrom"`
Output:
```"rotor" is an exact palindrome.
"été" is an exact palindrome.
"αννα" is an exact palindrome.
"salÃ las" is an inexact palindrome.
"In girum imus nocte et consumimur igni" is an inexact palindrome.
"Esope reste ici et se repose" is an inexact palindrome.
"This is a palindrom" is not a palindrome.```

## Objeck

` bundle Default {  class Test {    function : Main(args : String[]) ~ Nil {      IsPalindrome("aasa")->PrintLine();      IsPalindrome("acbca")->PrintLine();      IsPalindrome("xx")->PrintLine();    }     function : native : IsPalindrome(s : String) ~ Bool {      l := s->Size();      for(i := 0; i < l / 2; i += 1;) {        if(s->Get(i) <> s->Get(l - i - 1)) {          return false;        };      };       return true;    }  }} `

## OCaml

`let is_palindrome s =    let l = String.length s in    let rec comp n =        n = 0 || (s.[l-n] = s.[n-1] && comp (n-1)) in    comp (l / 2)`

and here a function to remove the white spaces in the string:

`let rem_space str =  let len = String.length str in  let res = Bytes.create len in  let rec aux i j =    if i >= len    then (Bytes.sub_string res 0 j)    else match str.[i] with      | ' ' | '\n' | '\t' | '\r' ->        aux (i+1) (j)      | _ ->        Bytes.set res j str.[i];        aux (i+1) (j+1)  in  aux 0 0 `

and to make the test case insensitive, just use the function String.lowercase_ascii.

## Octave

Recursive

`function v = palindro_r(s)  if ( length(s) == 1 )    v = true;    return;  elseif ( length(s) == 2 )    v = s(1) == s(2);    return;  endif  if ( s(1) == s(length(s)) )    v = palindro_r(s(2:length(s)-1));  else    v = false;  endifendfunction`

Non-recursive

`function v = palindro(s)  v = all( (s == s(length(s):-1:1)) == 1);endfunction`

Testing

`palindro_r("ingirumimusnocteetconsumimurigni")palindro("satorarepotenetoperarotas")`

## Oforth

`String method: isPalindrome  self reverse self == ;`

## Ol

` ; simple case - only lowercase letters(define (palindrome? str)   (let ((l (string->runes str)))      (equal? l (reverse l)))) (print (palindrome? "ingirumimusnocteetconsumimurigni")); ==> #true(print (palindrome? "thisisnotapalindrome")); ==> #false  ; complex case - with ignoring letter case and punctuation(define (alpha? x)   (<= #\a x #\z))(define (lowercase x)   (if (<= #\A x #\Z)      (- x (- #\A #\a))      x)) (define (palindrome? str)   (let ((l (filter alpha? (map lowercase (string->runes str)))))      (equal? l (reverse l)))) (print (palindrome? "A man, a plan, a cat, a ham, a yak, a yam, a hat, a canal-Panama!")); ==> #true(print (palindrome? "This is not a palindrome")); ==> #false `

## Oz

`fun {IsPalindrome S}  {Reverse S} == Send`

## PARI/GP

`ispal(s)={  s=Vec(s);  for(i=1,#v\2,    if(v[i]!=v[#v-i+1],return(0))  );  1};`

A version for numbers:

Works with: PARI/GP version 2.6.0 and above
`ispal(s)={  my(d=digits(n));  for(i=1,#d\2,    if(d[i]!=d[n+1=i],return(0))  );  1};`

## Pascal

Works with: Free Pascal
`program Palindro; { RECURSIVE }function is_palindro_r(s : String) : Boolean;begin   if length(s) <= 1 then      is_palindro_r := true   else begin      if s[1] = s[length(s)] then	 is_palindro_r := is_palindro_r(copy(s, 2, length(s)-2))      else	 is_palindro_r := false   endend; { is_palindro_r } { NON RECURSIVE; see [[Reversing a string]] for "reverse" }function is_palindro(s : String) : Boolean;begin   if s = reverse(s) then      is_palindro := true   else      is_palindro := falseend;`
`procedure test_r(s : String; r : Boolean);begin   write('"', s, '" is ');   if ( not r ) then      write('not ');   writeln('palindrome')end; var   s1, s2 : String; begin   s1 := 'ingirumimusnocteetconsumimurigni';   s2 := 'in girum imus nocte';   test_r(s1, is_palindro_r(s1));   test_r(s2, is_palindro_r(s2));   test_r(s1, is_palindro(s1));   test_r(s2, is_palindro(s2))end.`
`program PalindromeDetection;var  input, output: string;  s: char; i: integer;begin  writeln('write down your input:');  readln(input);  output:='';  for i:=1 to length(input) do  begin    s:=input[i];    output:=s+output;  end;  writeln('');  if(input=output)then  writeln('input was palindrome')  else  writeln('input was not palindrome');end.`

## Perl

There is more than one way to do this.

• palindrome uses the built-in function reverse().
• palindrome_c uses iteration; it is a translation of the C solution.
• palindrome_r uses recursion.
• palindrome_e uses a recursive regular expression.

All of these functions take a parameter, or default to \$_ if there is no parameter. None of these functions ignore case or strip characters; if you want do that, you can use (\$s = lc \$s) =~ s/[\W_]//g before you call these functions.

`# Palindrome.pmpackage Palindrome; use strict;use warnings; use Exporter 'import';our @EXPORT = qw(palindrome palindrome_c palindrome_r palindrome_e); sub palindrome{    my \$s = (@_ ? shift : \$_);    return \$s eq reverse \$s;} sub palindrome_c{    my \$s = (@_ ? shift : \$_);    for my \$i (0 .. length(\$s) >> 1)    {        return 0 unless substr(\$s, \$i, 1) eq substr(\$s, -1 - \$i, 1);    }    return 1;} sub palindrome_r{    my \$s = (@_ ? shift : \$_);    if (length \$s <= 1) { return 1; }    elsif (substr(\$s, 0, 1) ne substr(\$s, -1, 1)) { return 0; }    else { return palindrome_r(substr(\$s, 1, -1)); }} sub palindrome_e{    (@_ ? shift : \$_) =~ /^(.?|(.)(?1)\2)\$/ + 0}`

This example shows how to use the functions:

`# pbench.pluse strict;use warnings; use Benchmark qw(cmpthese);use Palindrome; printf("%d, %d, %d, %d: %s\n",       palindrome, palindrome_c, palindrome_r, palindrome_e, \$_)for    qw/a aa ab abba aBbA abca abba1 1abba    ingirumimusnocteetconsumimurigni/,    'ab cc ba',	'ab ccb a'; printf "\n"; my \$latin = "ingirumimusnocteetconsumimurigni";cmpthese(100_000, {    palindrome => sub { palindrome \$latin },    palindrome_c => sub { palindrome_c \$latin },    palindrome_r => sub { palindrome_r \$latin },    palindrome_e => sub { palindrome_e \$latin },});`
Output:
on a machine running Perl 5.10.1 on amd64-openbsd:
```\$ perl pbench.pl
1, 1, 1, 1: a
1, 1, 1, 1: aa
0, 0, 0, 0: ab
1, 1, 1, 1: abba
0, 0, 0, 0: aBbA
0, 0, 0, 0: abca
0, 0, 0, 0: abba1
0, 0, 0, 0: 1abba
1, 1, 1, 1: ingirumimusnocteetconsumimurigni
1, 1, 1, 1: ab cc ba
0, 0, 0, 0: ab ccb a

(warning: too few iterations for a reliable count)
Rate palindrome_r palindrome_e palindrome_c   palindrome
palindrome_r   51020/s           --         -50%         -70%         -97%
palindrome_e  102041/s         100%           --         -41%         -94%
palindrome_c  172414/s         238%          69%           --         -90%
palindrome   1666667/s        3167%        1533%         867%           --```

With this machine, palindrome() ran far faster than the alternatives (and too fast for a reliable count). The Perl regular expression engine recursed twice as fast as the Perl interpreter.

## Phix

```function is_palindrome(sequence s)
return s==reverse(s)
end function

?is_palindrome("rotator") -- prints 1
?is_palindrome("tractor") -- prints 0

constant punctuation = " `[email protected]#\$%^&*()-=_+[]{}\\|;:',.<>/?",
nulls = repeat("",length(punctuation))

function extra_credit(sequence s)
s = utf8_to_utf32(lower(substitute_all(s,punctuation,nulls)))
return s==reverse(s)
end function

-- these all print 1 (true)
?extra_credit("A man, a plan, a canal: Panama!")
?extra_credit("In girum imus nocte et consumimur igni")
?extra_credit("人人為我,我為人人")
?extra_credit("Я иду с мечем, судия")
?extra_credit("아들딸들아")
?extra_credit("가련하시다 사장집 아들딸들아 집장사 다시 하련가")
?extra_credit("tregða, gón, reiði - er nóg að gert")
```

## PHP

`<?phpfunction is_palindrome(\$string) {  return \$string == strrev(\$string);}?>`

Regular expression-based solution (source)

`<?phpfunction is_palindrome(\$string) {  return preg_match('/^(?:(.)(?=.*(\1(?(2)\2|))\$))*.?\2?\$/', \$string);}?>`

## Picat

`go =>   Tests = ["In girum imus nocte et consumimur igni",             "this is a non palindrome string",            "anna ABcdcBA anna",            "anna ABcdcBA annax",            "A man, a plan, a canoe, pasta, heros, rajahs" ++            "a coloratura, maps, snipe, percale, macaroni, " ++            "a gag, a banana bag, a tan, a tag, " ++            "a banana bag again (or a camel), a crepe, pins, " ++            "Spam, a rut, a Rolo, cash, a jar, sore hats, " ++            "a peon, a canal - Panama!",            10,            111111,            12221,            9384212,            10.01           ],    foreach(Test in Tests)      if is_palindrome(Test) then        println([Test, "exact palindrome"])     elseif is_palindrome_inexact(Test) then        println([Test, "inexact palindrome"])     else        println([Test, "no"])     end   end,   nl. % Detect palindromes for strings (and numbers).is_palindrome(N), number(N) => is_palindrome(N.to_string()).is_palindrome(S) => S == S.reverse(). % Detect inexact palindromes.is_palindrome_inexact(N), number(N) => is_palindrome_inexact(N.to_string()).is_palindrome_inexact(S) =>    is_palindrome(strip(S)).  % convert to lowercase and% skips punctuation and white space. strip(S) = [C : C in S.to_lowercase(),            not C.membchk("!?,.;-_ \t\n()[]{}")].`
Output:
```[In girum imus nocte et consumimur igni,inexact palindrome]
[this is a non palindrome string,no]
[anna ABcdcBA anna,exact palindrome]
[anna ABcdcBA annax,no]
[A man, a plan, a canoe, pasta, heros, rajahsa coloratura, maps, snipe, percale, macaroni, a gag, a banana bag, a tan, a tag, a banana bag again (or a camel), a crepe, pins, Spam, a rut, a Rolo, cash, a jar, sore hats, a peon, a canal - Panama!,inexact palindrome]
[10,no]
[11,exact palindrome]
[111111,exact palindrome]
[12221,exact palindrome]
[9384212,no]
[10.01,exact palindrome]```

## PicoLisp

`(de palindrome? (S)   (= (setq S (chop S)) (reverse S)) )`
Output:
```: (palindrome? "ingirumimusnocteetconsumimurigni")
-> T```

## Pike

`int main(){   if(pal("rotator")){      write("palindrome!\n");   }   if(!pal("asdf")){      write("asdf isn't a palindrome.\n");   }} int pal(string input){   if( reverse(input) == input ){      return 1;   } else {      return 0;   }}`

## PL/I

To satisfy the revised specification (which contradicts the preceding explanation) the following trivially solves the problem in PL/I:

`is_palindrome = (text = reverse(text));`

The following solution strips spaces:

`is_palindrome: procedure (text) returns (bit(1));   declare text character (*) varying;    text = remove_blanks(text);   text = lowercase(text);   return (text = reverse(text)); remove_blanks: procedure (text);   declare text character (*) varying;   declare (i, j) fixed binary (31);   j = 0;   do i = 1 to length(text);      if substr(text, i, 1) = ' ' then         do; j = j + 1; substr(text, j, 1) = substr(text, i, 1); end;   end;   return (substr(text, 1, j));end remove_blanks;end is_palindrome;`

## PL/M

`100H: /* CHECK EXACT PALINDROME ASSUMING \$-TERMINATED STRING */PALINDROME: PROCEDURE(PTR) BYTE;    DECLARE (PTR, FRONT, BACK) ADDRESS, STR BASED PTR BYTE;     /* FIND END */    FRONT, BACK = 0;    DO WHILE STR(BACK) <> '\$';        BACK = BACK + 1;    END;    BACK = BACK - 1;     /* CHECK MATCH */    DO WHILE (FRONT < BACK) AND (STR(FRONT) = STR(BACK));        FRONT = FRONT + 1;        BACK = BACK - 1;    END;     RETURN FRONT >= BACK;END PALINDROME; /* CHECK INEXACT PALINDROME: FILTER OUT NON-LETTERS AND NUMBERS */INEXACT\$PALINDROME: PROCEDURE(PTR) BYTE;    /* 256 BYTES OUGHT TO BE ENOUGH FOR EVERYONE */    DECLARE (PTR, OPTR) ADDRESS;    DECLARE FILTER (256) BYTE;    DECLARE (IN BASED PTR, OUT BASED OPTR) BYTE;    OPTR = .FILTER;     DO WHILE IN <> '\$';        OUT = IN OR 32;        /* LOWERCASE CHARACTERS ARE NOT IN THE PL/M CHARSET,           BUT WE CAN JUST WRITE THE ASCII VALUES AS NUMBERS */        IF (OUT >= '0' AND OUT <= '9')        OR (OUT >= 97  AND OUT <= 122) THEN            OPTR = OPTR + 1;        PTR = PTR + 1;    END;    OUT = '\$';     RETURN PALINDROME(.FILTER);END INEXACT\$PALINDROME; /* CP/M BDOS CALLS */BDOS: PROCEDURE(FUNC, ARG);    DECLARE FUNC BYTE, ARG ADDRESS;    GO TO 5;END BDOS; PRINT: PROCEDURE(STRING);    DECLARE STRING ADDRESS;    CALL BDOS(9, STRING);END PRINT; /* TEST SOME STRINGS */DECLARE STRINGS (8) ADDRESS;STRINGS(0) = .'ROTOR\$';STRINGS(1) = .'RACECAR\$';STRINGS(2) = .'LEVEL\$';STRINGS(3) = .'REDDER\$';STRINGS(4) = .'RACECAR\$';STRINGS(5) = .'A MAN, A PLAN, A CANAL: PANAMA\$';STRINGS(6) = .'EGAD, A BASE TONE DENOTES A BAD AGE.\$';STRINGS(7) = .'ROSETTA\$'; DECLARE N BYTE;DO N = 0 TO LAST(STRINGS);    CALL PRINT(STRINGS(N));    CALL PRINT(.': \$');    IF PALINDROME(STRINGS(N)) THEN        CALL PRINT(.'EXACT\$');    ELSE IF INEXACT\$PALINDROME(STRINGS(N)) THEN        CALL PRINT(.'INEXACT\$');    ELSE        CALL PRINT(.'NOT A PALINDROME\$');    CALL PRINT(.(13,10,'\$'));END; CALL BDOS(0,0);EOF`
Output:
```ROTOR: EXACT
RACECAR: EXACT
LEVEL: EXACT
REDDER: EXACT
RACECAR: EXACT
A MAN, A PLAN, A CANAL: PANAMA: INEXACT
ROSETTA: NOT A PALINDROME```

## Plain English

Strings and substrings all come with two byte pointers by default:

• `first`, which points to the first byte in the string.
• `last`, which points to the last byte in the string.

`first` is an address, while `first's target` is the byte at that address. No need to actually reverse the string; just compare the first's target with the last's target until they meet in the middle.

`To decide if a string is palindromic:Slap a substring on the string.Loop.If the substring's first is greater than the substring's last, say yes.If the substring's first's target is not the substring's last's target, say no.Add 1 to the substring's first.Subtract 1 from the substring's last.Repeat.`

## Pointless

Basic Function

`isPalindrome(chars) =  chars == reverse(chars)`

With Pre-processing

`output =  "A man, a plan, a canal -- Panama"  |> toList  |> filter(inFunc(alNums))  |> map(toLower)  |> isPalindrome  |> println`
Output:
`true`

## Potion

`# The readable recursive versionpalindrome_i = (s, b, e):  if (e <= b): true.  elsif (s ord(b) != s ord(e)): false.  else: palindrome_i(s, b+1, e-1).. palindrome = (s):  palindrome_i(s, 0, s length - 1). palindrome(argv(1))`

## PowerBASIC

The output is identical to the QBasic version, above.

`FUNCTION isPalindrome (what AS STRING) AS LONG    DIM whatcopy AS STRING, chk AS STRING, tmp AS STRING * 1, L0 AS LONG     FOR L0 = 1 TO LEN(what)        tmp = UCASE\$(MID\$(what, L0, 1))        SELECT CASE tmp            CASE "A" TO "Z"                whatcopy = whatcopy & tmp                chk = tmp & chk            CASE "0" TO "9"                MSGBOX "Numbers are cheating! (""" & what & """)"                FUNCTION = 0                EXIT FUNCTION        END SELECT    NEXT     FUNCTION = ISTRUE((whatcopy) = chk)END FUNCTION  FUNCTION PBMAIN () AS LONG    DATA "My dog has fleas", "Madam, I'm Adam.", "1 on 1", "In girum imus nocte et consumimur igni"    DIM L1 AS LONG, w AS STRING    FOR L1 = 1 TO DATACOUNT        w = READ\$(L1)        IF ISTRUE(isPalindrome(w)) THEN            MSGBOX \$DQ & w & """ is a palindrome"        ELSE            MSGBOX \$DQ & w & """ is not a palindrome"        END IF    NEXTEND FUNCTION`

## PowerShell

An exact version based on reversing the string:

` Function Test-Palindrome( [String] \$Text ){    \$CharArray = \$Text.ToCharArray()    [Array]::Reverse(\$CharArray)    \$Text -eq [string]::join('', \$CharArray)} `

### PowerShell (Regex Version)

This version is much faster because it does not manipulate arrays. [This is not clear; the above version was slowed down by using -join instead of [string]::join, and -like instead of -eq. After changing those it is similar, if not faster, than this version].

` function Test-Palindrome{  <#    .SYNOPSIS        Tests if a string is a palindrome.    .DESCRIPTION        Tests if a string is a true palindrome or, optionally, an inexact palindrome.    .EXAMPLE        Test-Palindrome -Text "racecar"    .EXAMPLE        Test-Palindrome -Text '"Deliver desserts," demanded Nemesis, "emended, named, stressed, reviled."' -Inexact  #>    [CmdletBinding()]    [OutputType([bool])]    Param    (        # The string to test for palindrominity.        [Parameter(Mandatory=\$true)]        [string]        \$Text,         # When specified, detects an inexact palindrome.        [switch]        \$Inexact    )     if (\$Inexact)    {        # Strip all punctuation and spaces        \$Text = [Regex]::Replace("\$Text(\$7&","[^1-9a-zA-Z]","")    }     \$Text -match "^(?'char'[a-z])+[a-z]?(?:\k'char'(?'-char'))+(?(char)(?!))\$"} `
` Test-Palindrome -Text 'radar' `
Output:
```True
```
` Test-Palindrome -Text "In girum imus nocte et consumimur igni." `
Output:
```False
```
` Test-Palindrome -Text "In girum imus nocte et consumimur igni." -Inexact `
Output:
```True
```

### PowerShell (Unicode category aware, no string reverse)

An inexact version can remove punctuation by looking at Unicode categories for each character, either using .Net methods or a regex.

`Function Test-Palindrome {[CmdletBinding()]Param(    [Parameter(ValueFromPipeline)]    [string[]]\$Text) process {    :stringLoop foreach (\$T in \$Text)    {        # Normalize Unicode combining characters,        # so character á compares the same as (a+combining accent)        \$T = \$T.Normalize([Text.NormalizationForm]::FormC)         # Remove anything from outside the Unicode category        # "Letter from any language"        \$T = \$T -replace '\P{L}', ''         # Walk from each end of the string inwards,         # comparing a char at a time.        # Avoids string copy / reverse overheads.        \$Left, \$Right = 0, [math]::Max(0, (\$T.Length - 1))        while (\$Left -lt \$Right)        {            if (\$T[\$Left] -ne \$T[\$Right])            {                # return early if string is not a palindrome                [PSCustomObject]@{                    Text = \$T                    IsPalindrome = \$False                }                continue stringLoop            }            else            {                \$Left++                \$Right--            }        }         # made it to here, then string is a palindrome        [PSCustomObject]@{            Text = \$T            IsPalindrome = \$True        }     }}}'ánu-ná', 'nowt' | Test-Palindrome`
Output:
```PS C:\> 'ánu-ná', 'nowt' | Test-Palindrome

Text  IsPalindrome
----  ------------
ánuná         True
now          False
```

## Processing

` void setup(){	println(isPalindrome(InsertPalindromeHere));} boolean isPalindrome(string check){	char[] letters = new char[check.length];	string invert = " ";	string modCheck = " " + check;	for(int i = 0; i < letters.length; i++){		letters[i] = check.charAt(i);	}	for(int i = letters.length-1; i >= 0; i--){		invert = invert + letters[i];	} 	if(invert == modCheck){		return true;	} else {		return false;	}} `
Output:
```"true" or "false" depending
```

#### Alternative Implementation: using StringBuilder, implementing exact and inexact check

` void setup(){    println("PalindromeDetection");     String[] tests = {        "abcba",        "aa",        "a",        "",        " ",        "ab",        "abcdba",        "A man, a plan, a canal: Panama!",        "Dammit, I’m Mad!",        "Never odd or even",        "ingirumimusnocteetconsumimurigni"    };     for (int i = 0; i < tests.length; i++){        println((i + 1) + ". '" + tests[i] + "' isExactPalindrome: " + isExactPalindrome(tests[i]) + " isInexactPalindrome: " + isInexactPalindrome(tests[i]));    }} /** Check for exact palindrome using StringBuilder and String since String in Java does not provide any reverse functionality because Strings are immutable.*/boolean isExactPalindrome(String s){	StringBuilder sb = new StringBuilder(s);	return s.equals(sb.reverse().toString());} /** Check for inexact palindrome using the check for exact palindromeabove.*/boolean isInexactPalindrome(String s){    // removes all whitespaces and non-visible characters,     // remove anything besides alphabet characters    // ignore case    return isExactPalindrome(s.replaceAll("\\s+","").replaceAll("[^A-Za-z]+", "").toLowerCase());} `
Output:
```PalindromeDetection
1. 'abcba' isExactPalindrome: true isInexactPalindrome: true
2. 'aa' isExactPalindrome: true isInexactPalindrome: true
3. 'a' isExactPalindrome: true isInexactPalindrome: true
4. '' isExactPalindrome: true isInexactPalindrome: true
5. ' ' isExactPalindrome: true isInexactPalindrome: true
6. 'ab' isExactPalindrome: false isInexactPalindrome: false
7. 'abcdba' isExactPalindrome: false isInexactPalindrome: false
8. 'A man, a plan, a canal: Panama!' isExactPalindrome: false isInexactPalindrome: true
9. 'Dammit, I’m Mad!' isExactPalindrome: false isInexactPalindrome: true
10. 'Never odd or even' isExactPalindrome: false isInexactPalindrome: true
11. 'ingirumimusnocteetconsumimurigni' isExactPalindrome: true isInexactPalindrome: true
```

## Prolog

Non-recursive

From this tutorial.

`palindrome(Word) :- name(Word,List), reverse(List,List).`

Recursive

Works with: SWI Prolog
`pali(Str) :- sub_string(Str, 0, 1, _, X), string_concat(Str2, X, Str), string_concat(X, Mid, Str2), pali(Mid).pali(Str) :- string_length(Str, Len), Len < 2.`

Changing string into atom makes the program run also on GNU Prolog. I.e.

Works with: GNU Prolog
`pali(Str) :- sub_atom(Str, 0, 1, _, X), atom_concat(Str2, X, Str), atom_concat(X, Mid, Str2), pali(Mid).pali(Str) :- atom_length(Str, Len), Len < 2.`

## PureBasic

Works with: PureBasic version 4.41
`Procedure IsPalindrome(StringToTest.s)  If StringToTest=ReverseString(StringToTest)    ProcedureReturn 1  Else    ProcedureReturn 0  EndIfEndProcedure`

## Python

Now that Python 2.7 and Python 3.4 are quite different, We should include the version IMHO.

Non-recursive

This one uses the reversing the string technique (to reverse a string Python can use the odd but right syntax string[::-1])

`def is_palindrome(s):  return s == s[::-1]`

Non-recursive, Ignoring Punctuation/Case/Spaces

A word is a palindrome if the letters are the same forwards as backwards, but the other methods given here will return False for, e.g., an input of "Go hang a salami, I'm a lasagna hog" or "A man, a plan, a canal: Panama." An implementation that traverses the string and ignores case differences, spaces, and non-alpha characters is pretty trivial.

`def is_palindrome(s):  low = 0  high = len(s) - 1  while low < high:    if not s[low].isalpha():      low += 1    elif not s[high].isalpha():      high -= 1    else:      if s[low].lower() != s[high].lower():        return False      else:        low += 1        high -= 1        return True`

Recursive

`def is_palindrome_r(s):  if len(s) <= 1:    return True  elif s[0] != s[-1]:    return False  else:    return is_palindrome_r(s[1:-1])`

Python has short-circuit evaluation of Boolean operations so a shorter and still easy to understand recursive function is

`def is_palindrome_r2(s):  return not s or s[0] == s[-1] and is_palindrome_r2(s[1:-1])`

Testing

`def test(f, good, bad):  assert all(f(x) for x in good)  assert not any(f(x) for x in bad)  print '%s passed all %d tests' % (f.__name__, len(good)+len(bad)) pals = ('', 'a', 'aa', 'aba', 'abba')notpals = ('aA', 'abA', 'abxBa', 'abxxBa')for ispal in is_palindrome, is_palindrome_r, is_palindrome_r2:  test(ispal, pals, notpals)`

Palindrome Using Regular Expressions Python 2.7

`def p_loop():  import re, string  re1=""       # Beginning of Regex  re2=""       # End of Regex  pal=raw_input("Please Enter a word or phrase: ")  pd = pal.replace(' ','')  for c in string.punctuation:     pd = pd.replace(c,"")  if pal == "" :    return -1  c=len(pd)   # Count of chars.  loops = (c+1)/2   for x in range(loops):    re1 = re1 + "(\w)"    if (c%2 == 1 and x == 0):       continue     p = loops - x    re2 = re2 + "\\" + str(p)  regex= re1+re2+"\$"   # regex is like "(\w)(\w)(\w)\2\1\$"  #print(regex)  # To test regex before re.search  m = re.search(r'^'+regex,pd,re.IGNORECASE)  if (m):     print("\n   "+'"'+pal+'"')     print("   is a Palindrome\n")     return 1  else:     print("Nope!")     return 0`

Checking the left half against a reflection of the right half

`'''Palindrome detection'''  # isPalindrome :: String -> Booldef isPalindrome(s):    '''True if the string is unchanged under reversal.       (The left half is a reflection of the right half)    '''    d, m = divmod(len(s), 2)    return s[0:d] == s[d + m:][::-1]  # ------------------------- TEST -------------------------# main :: IO ()def main():    '''Test'''     print('\n'.join(        f'{repr(s)} -> {isPalindrome(cleaned(s))}' for s in [            "",            "a",            "ab",            "aba",            "abba",            "In girum imus nocte et consumimur igni"        ]    ))  # cleaned :: String -> Stringdef cleaned(s):    '''A lower-case copy of s, with spaces pruned.'''    return [c.lower() for c in s if ' ' != c]  # MAIN ---if __name__ == '__main__':    main() `
Output:
```'' -> True
'a' -> True
'ab' -> False
'aba' -> True
'abba' -> True
'In girum imus nocte et consumimur igni' -> True```

Twiddle Indexing

I have no idea what this technique is called, so I'm going with "Twiddle Indexing".

```   Twiddle Indexing v. Negative Indexing

0  1  2  3  4   <-- index
[ a, b, c, d, e ]
~4 ~3 ~2 ~1 ~0   <-- twiddle index

0  1  2  3  4   <-- index
[ a, b, c, d, e ]
-5 -4 -3 -2 -1   <-- negative index```
`def palindromic(str):    for i in range(len(str)//2):        if str[i] != str[~i]:            return(False)    return(True)`

## Quackery

`  [ dup reverse = ]        is palindromic       ( [ --> b )   [ [] swap witheach      [ upper dup         dup lower = iff          drop else join ]      palindromic ]         is inexactpalindrome ( \$ --> b )`

### Twiddle Indexing

`  [ true swap     dup size 2 / times       [ dup i peek         over i ~ peek != if           [ dip not conclude ] ]     drop ]                       is palindromic ( [ --> b )`

## R

Recursive

Note that the recursive method will fail if the string length is too long. R will assume an infinite recursion if a recursion nests deeper than 5,000. Options may be set in the environment to increase this to 500,000.

`palindro <- function(p) {  if ( nchar(p) == 1 ) {    return(TRUE)  } else if ( nchar(p) == 2 ) {    return(substr(p,1,1) == substr(p,2,2))  } else {    if ( substr(p,1,1) == substr(p, nchar(p), nchar(p)) ) {      return(palindro(substr(p, 2, nchar(p)-1)))    } else {      return(FALSE)    }  }}`

Iterative

`palindroi <- function(p) {  for(i in 1:floor(nchar(p)/2) ) {    r <- nchar(p) - i + 1    if ( substr(p, i, i) != substr(p, r, r) ) return(FALSE)   }  TRUE}`

Comparative

This method is somewhat faster than the other two.

Note that this method incorrectly regards an empty string as not a palindrome. Please leave this bug in the code, and take a look a the Testing_a_Function page.

`revstring <- function(stringtorev) {   return(      paste(           strsplit(stringtorev,"")[[1]][nchar(stringtorev):1]           ,collapse="")           )}palindroc <- function(p) {return(revstring(p)==p)}`

Rev

R has a built-in function for reversing vectors, so we only have to coerce our input in to the proper form.

Unicode is supported, but this ignores the "inexact palindromes" extra credit requirement because, without some sort of regex, supporting Unicode while stripping punctuation and white space is hard in R.

`is.Palindrome <- function(string){  characters <- unlist(strsplit(string, ""))  all(characters == rev(characters))}`
Output:

The rev solution is not benchmarked.

```test <- "ingirumimusnocteetconsumimurigni"
tester <- paste(rep(test,38),collapse="")
> test <- "ingirumimusnocteetconsumimurigni"
> tester <- paste(rep(test,38),collapse="")
> system.time(palindro(tester))
user  system elapsed
0.04    0.00    0.04
> system.time(palindroi(tester))
user  system elapsed
0.01    0.00    0.02
> system.time(palindroc(tester))
user  system elapsed
0       0       0
```

## Racket

` (define (palindromb str)  (let* ([lst (string->list (string-downcase str))]         [slst (remove* '(#\space) lst)])    (string=? (list->string (reverse slst)) (list->string slst)))) ;;example output > (palindromb "able was i ere i saw elba")#t> (palindromb "waht the hey")#f> (palindromb "In girum imus nocte et consumimur igni")#t>  `

## Raku

(formerly Perl 6)

`subset Palindrom of Str where {    .flip eq \$_ given .comb(/\w+/).join.lc} my @tests = q:to/END/.lines;    A man, a plan, a canal: Panama.    My dog has fleas    Madam, I'm Adam.    1 on 1    In girum imus nocte et consumimur igni    END for @tests { say \$_ ~~ Palindrom, "\t", \$_ }`
Output:
```True	A man, a plan, a canal: Panama.
False	My dog has fleas
False	1 on 1
True	In girum imus nocte et consumimur igni
```

## Rascal

The most simple solution:

`import String; public bool palindrome(str text) =  toLowerCase(text) == reverse(text);`

A solution that handles sentences with spaces and capitals:

`import String; public bool palindrome(str text){	text = replaceAll(toLowerCase(text), " ", "");	return text == reverse(text);} `

Example:

`rascal>palindrome("In girum imus nocte et consumimur igni")bool: true`

## REBOL

`rebol [    Title: "Palindrome Recognizer"    URL: http://rosettacode.org/wiki/Palindrome] ; In order to compete with all the one-liners, the operation is; compressed: parens force left hand side to evaluate first, where I; copy the phrase, then uppercase it and assign it to 'p'. Now the; right hand side is evaluated: p is copied, then reversed in place;; the comparison is made and implicitely returned. palindrome?: func [	phrase [string!] "Potentially palindromatic prose."	/local p][(p: uppercase copy phrase) = reverse copy p] ; Teeny Tiny Test Suite assert: func [code][print [either do code ["  ok"]["FAIL"]  mold code]] print "Simple palindromes, with an exception for variety:"repeat phrase ["z" "aha" "sees" "oofoe" "Deified"][	assert compose [palindrome? (phrase)]] print [crlf "According to the problem statement, these should fail:"]assert [palindrome? "A man, a plan, a canal, Panama."] ; Punctuation not ignored.assert [palindrome? "In girum imus nocte et consumimur igni"] ; Spaces not removed. ; I know we're doing palindromes, not alliteration, but who could resist...?`
Output:
```Simple palindromes, with an exception for variety:
ok [palindrome? "z"]
ok [palindrome? "aha"]
ok [palindrome? "sees"]
FAIL [palindrome? "oofoe"]
ok [palindrome? "Deified"]

According to the problem statement, these should fail:
FAIL [palindrome? "A man, a plan, a canal, Panama."]
FAIL [palindrome? "In girum imus nocte et consumimur igni"]```

## Retro

` :palindrome? (s-f) dup s:hash [ s:reverse s:hash ] dip eq? ; 'ingirumimusnocteetconsumimurigni palindrome? n:put `

## REXX

### version 1

`/*REXX pgm checks if phrase is palindromic; ignores the case of the letters.  */parse arg y                            /*get (optional) phrase from the C.L.  */if y=''  then y='In girum imus nocte et consumimur igni'    /*[↓] translation.*/               /*We walk around in the night and we are burnt by the fire (of love).*/say 'string = ' yif isTpal(y)  then                   say 'The string is a true palindrome.'              else if isPal(y)  then say 'The string is an inexact palindrome.'                                else say "The string isn't palindromic."exit                                   /*stick a fork in it,  we're all done. *//*────────────────────────────────────────────────────────────────────────────*/isTpal:  return reverse(arg(1))==arg(1)isPal:   return isTpal(translate(space(x,0)))`
output :
```string =  In girum imus nocte et consumimur igni
The string is an inexact palindrome.
```

### version 2

Works with: ARexx
Works with: Regina

(Works with Regina 3.8 and later, with options: AREXX_BIFS and AREXX_SEMANTICS)

It should be noted that the   COMPRESS   function is not a Classic REXX BIF and isn't present in many REXXes.
The   SPACE(string,0)   BIF can be used instead.

It should also be noted that   UPPER   BIF is not present in some REXXes.
Use the   PARSE UPPER   statement or   TRANSLATE()   BIF instead.

` /* REXX */ /*Check whether a string is a palindrome */parse pull stringselect	when palindrome(string) then say string 'is an exact palindrome.'	when palindrome(compress(upper(string))) then say string 'is an inexact palindrome.'	otherwise say string 'is not palindromic.'	endexit 0 palindrome: procedureparse arg stringreturn string==reverse(string) `
Output:
```ABBA is an exact palindrome.
In girum imus nocte et consumimur igni is an inexact palindrome.
djdjdj is not palindromic.
```

## Ring

` aString = "radar"bString = ""for i=len(aString) to 1 step -1    bString = bString + aString[i]nextsee aStringif aString = bString see " is a palindrome." + nlelse see " is not a palindrome" + nl ok `

## Ruby

Non-recursive

`def palindrome?(s)  s == s.reverseend`

Recursive

`def r_palindrome?(s)  if s.length <= 1    true  elsif s[0] != s[-1]    false  else    r_palindrome?(s[1..-2])  endend`

Testing Note that the recursive method is much slower -- using the 2151 character palindrome by Dan Hoey here, we have:

`str = "A man, a plan, a caret, [...2110 chars deleted...] a canal--Panama.".downcase.delete('^a-z')puts palindrome?(str)    # => trueputs r_palindrome?(str)  # => true require 'benchmark'Benchmark.bm do |b|  b.report('iterative') {10000.times {palindrome?(str)}}  b.report('recursive') {10000.times {r_palindrome?(str)}}end`
Output:
```true
true
user     system      total        real
iterative  0.062000   0.000000   0.062000 (  0.055000)
recursive 16.516000   0.000000  16.516000 ( 16.562000)```

## Run BASIC

`data "My dog has fleas", "Madam, I'm Adam.", "1 on 1", "In girum imus nocte et consumimur igni" for i = 1 to 4  read w\$  print w\$;" is ";isPalindrome\$(w\$);" Palindrome"next FUNCTION isPalindrome\$(str\$)for i = 1 to len(str\$)  a\$ = upper\$(mid\$(str\$,i,1))   if (a\$ >= "A" and a\$ <= "Z") or (a\$ >= "0" and a\$ <= "9") then b\$ = b\$ + a\$: c\$ = a\$ + c\$next iif b\$ <> c\$ then isPalindrome\$ = "not"`
Output:
```My dog has fleas is not Palindrome
1 on 1 is not Palindrome
In girum imus nocte et consumimur igni is  Palindrome```

## Rust

`fn is_palindrome(string: &str) -> bool {    let half_len = string.len() / 2;    string        .chars()        .take(half_len)        .eq(string.chars().rev().take(half_len))} macro_rules! test {    ( \$( \$x:tt ),* ) => { \$( println!("'{}': {}", \$x, is_palindrome(\$x)); )* };} fn main() {    test!(        "",        "a",        "ada",        "adad",        "ingirumimusnocteetconsumimurigni",        "人人為我,我為人人",        "Я иду с мечем, судия",        "아들딸들아",        "The quick brown fox"    );}`
Output:
```'': true
'a': true
'ingirumimusnocteetconsumimurigni': true
'人人為我,我為人人': true
'Я иду с мечем, судия': false
'아들딸들아': true
'The quick brown fox': false
```

The above soluion checks if the codepoints form a pallindrome, but it is perhaps more correct to consider if the graphemes form a pallindrome. This can be accomplished with an external library and a slight modification to `is_palindrome`.

`extern crate unicode_segmentation;use unicode_segmentation::UnicodeSegmentation;fn is_palindrome(string: &str) -> bool {    string.graphemes(true).eq(string.graphemes(true).rev())}`

## SAS

Description

` The macro "palindro" has two parameters: string and ignorewhitespace.  string is the expression to be checked.  ignorewhitespace, (Y/N), determines whether or not to ignore blanks and punctuation.This macro was written in SAS 9.2.  If you use a version before SAS 9.1.3, the compress function options will not work. `

Code

` %MACRO palindro(string, ignorewhitespace);  DATA _NULL_;    %IF %UPCASE(&ignorewhitespace)=Y %THEN %DO;/* The arguments of COMPRESS (sp) ignore blanks and puncutation *//* We take the string and record it in reverse order using the REVERSE function. */      %LET rev=%SYSFUNC(REVERSE(%SYSFUNC(COMPRESS(&string,,sp))));       %LET string=%SYSFUNC(COMPRESS(&string.,,sp));    %END;     %ELSE %DO;      %LET rev=%SYSFUNC(REVERSE(&string));    %END;    /*%PUT rev=&rev.;*/    /*%PUT string=&string.;*/ /* Here we determine if the string and its reverse are the same. */    %IF %UPCASE(&string)=%UPCASE(&rev.) %THEN %DO;      %PUT TRUE;    %END;    %ELSE %DO;      %PUT FALSE;     %END;  RUN;%MEND; `

Example macro call and output

` %palindro("a man, a plan, a canal: panama",y); TRUE NOTE: DATA statement used (Total process time):      real time           0.00 seconds      cpu time            0.00 seconds %palindro("a man, a plan, a canal: panama",n); FALSE NOTE: DATA statement used (Total process time):      real time           0.00 seconds      cpu time            0.00 seconds `

## Scala

Library: Scala

### Non-recursive, robustified

`  def isPalindrome(s: String): Boolean = (s.size >= 2) && s == s.reverse`

### Bonus: Detect and account for odd space and punctuation

`  def isPalindromeSentence(s: String): Boolean =    (s.size >= 2) && {      val p = s.replaceAll("[^\\p{L}]", "").toLowerCase      p == p.reverse    } `

### Recursive

`import scala.annotation.tailrec   def isPalindromeRec(s: String) = {    @tailrec    def inner(s: String): Boolean =      (s.length <= 1) || (s.head == s.last) && inner(s.tail.init)     (s.size >= 2) && inner(s)  }`

Testing

`  // Testing  assert(!isPalindrome(""))  assert(!isPalindrome("z"))  assert(isPalindrome("amanaplanacanalpanama"))  assert(!isPalindrome("Test 1,2,3"))  assert(isPalindrome("1 2 1"))  assert(!isPalindrome("A man a plan a canal Panama."))   assert(!isPalindromeSentence(""))  assert(!isPalindromeSentence("z"))  assert(isPalindromeSentence("amanaplanacanalpanama"))  assert(!isPalindromeSentence("Test 1,2,3"))  assert(isPalindromeSentence("1 2 1"))  assert(isPalindromeSentence("A man a plan a canal Panama."))   assert(!isPalindromeRec(""))  assert(!isPalindromeRec("z"))  assert(isPalindromeRec("amanaplanacanalpanama"))  assert(!isPalindromeRec("Test 1,2,3"))  assert(isPalindromeRec("1 2 1"))  assert(!isPalindromeRec("A man a plan a canal Panama."))   println("Successfully completed without errors.")`

## Scheme

Non-recursive

`(define (palindrome? s)  (let ((chars (string->list s)))    (equal? chars (reverse chars))))`

Recursive

`(define (palindrome? s)  (let loop ((i 0)             (j (- (string-length s) 1)))    (or (>= i j)        (and (char=? (string-ref s i) (string-ref s j))             (loop (+ i 1) (- j 1)))))) ;; Or:(define (palindrome? s)  (let loop ((s (string->list s))             (r (reverse (string->list s))))    (or (null? s)        (and (char=? (car s) (car r))             (loop (cdr s) (cdr r)))))) > (palindrome? "ingirumimusnocteetconsumimurigni")#t> (palindrome? "This is not a palindrome")#f>`

## Seed7

`const func boolean: palindrome (in string: stri) is func  result    var boolean: isPalindrome is TRUE;  local    var integer: index is 0;    var integer: length is 0;  begin    length := length(stri);    for index range 1 to length div 2 do      if stri[index] <> stri[length - index + 1] then        isPalindrome := FALSE;      end if;    end for;  end func;`

For palindromes where spaces shuld be ignore use:

`palindrome(replace("in girum imus nocte et consumimur igni", " ", ""))`

## SequenceL

Using the Reverse Library Function

`import <Utilities/Sequence.sl>; isPalindrome(string(1)) := equalList(string, reverse(string));`

Version Using an Indexed Function

`isPalindrome(string(1)) :=	let		compares[i] := string[i] = string[size(string) - (i - 1)] foreach i within 1 ... (size(string) / 2);	in		all(compares);`

## Sidef

Built-in

`say "noon".is_palindrome;    # true`

Non-recursive

`func palindrome(s) {    s == s.reverse}`

Recursive

`func palindrome(s) {    if (s.len <= 1) {        true    }    elsif (s.first != s.last) {        false    }    else {        __FUNC__(s.ft(1, -2))    }}`

## Simula

`BEGIN     BOOLEAN PROCEDURE ISPALINDROME(T); TEXT T;    BEGIN        BOOLEAN RESULT;        INTEGER I, J;        I := 1;        J := T.LENGTH;        RESULT := TRUE;        WHILE RESULT AND I < J DO        BEGIN            CHARACTER L, R;            T.SETPOS(I); L := T.GETCHAR; I := I + 1;            T.SETPOS(J); R := T.GETCHAR; J := J - 1;            RESULT := L = R;        END;        ISPALINDROME := RESULT;    END ISPALINDROME;     TEXT T;    FOR T :- "", "A", "AA", "ABA", "SALALAS", "MADAMIMADAM",             "AB", "AAB", "ABCBDA"    DO    BEGIN        OUTTEXT(IF ISPALINDROME(T) THEN "IS   " ELSE "ISN'T");        OUTTEXT(" PALINDROME: ");        OUTCHAR('"');        OUTTEXT(T);        OUTCHAR('"');        OUTIMAGE;    END; END.`
Output:
```IS    PALINDROME: ""
IS    PALINDROME: "A"
IS    PALINDROME: "AA"
IS    PALINDROME: "ABA"
IS    PALINDROME: "SALALAS"
ISN'T PALINDROME: "AB"
ISN'T PALINDROME: "AAB"
ISN'T PALINDROME: "ABCBDA"
```

## Slate

Non-Recursive

`[email protected](String traits) isPalindrome[  (s lexicographicallyCompare: s reversed) isZero].`

Recursive Defined on Sequence since we are not using String-specific methods:

`[email protected](Sequence traits) isPalindrome[  s isEmpty    ifTrue: [True]    ifFalse: [(s first = s last) /\ [(s sliceFrom: 1 to: s indexLast - 1) isPalindrome]]].`

Testing

`define: #p -> 'ingirumimusnocteetconsumimurigni'.inform: 'sequence ' ; p ; ' is ' ; (p isPalindrome ifTrue: [''] ifFalse: ['not ']) ; 'a palindrome.'.`

## Smalltalk

Works with: Squeak
`isPalindrome := [:aString |	str := (aString select: [:chr| chr isAlphaNumeric]) collect: [:chr | chr asLowercase].	str = str reversed.	]. `
Works with: GNU Smalltalk
`String extend [  palindro [                  "Non-recursive"    ^ self = (self reverse)  ]  palindroR [                 "Recursive"    (self size) <= 1 ifTrue: [ ^true ]      ifFalse: [ |o i f| o := self asOrderedCollection.          i := o removeFirst.          f := o removeLast.          i = f ifTrue: [ ^ (o asString) palindroR ]                ifFalse: [ ^false ]       ]  ]].`

Testing

`('hello' palindro) printNl.('hello' palindroR) printNl.('ingirumimusnocteetconsumimurigni' palindro) printNl.('ingirumimusnocteetconsumimurigni' palindroR) printNl.`
`SequenceableCollection>>isPalindrome	^self reverse = self `

## SNOBOL4

`        define('pal(str)') :(pal_end)pal     str notany(&ucase &lcase) = :s(pal)        str = replace(str,&ucase,&lcase)        leq(str,reverse(str)) :s(return)f(freturn)pal_end         define('palchk(str)tf') :(palchk_end)palchk  output = str;         tf = 'False'; tf = pal(str) 'True'        output = 'Palindrome: ' tf :(return)palchk_end         *       # Test and display        palchk('Able was I ere I saw Elba')        palchk('In girum imus nocte et consumimur igni')        palchk('The quick brown fox jumped over the lazy dogs')end`
Output:
```Able was I ere I saw Elba
Palindrome: True
In girum imus nocte et consumimur igni
Palindrome: True
The quick brown fox jumped over the lazy dogs
Palindrome: False```

## SQL

`SET @txt = REPLACE('In girum imus nocte et consumimur igni', ' ', '');SELECT REVERSE(@txt) = @txt;`

## Swift

Works with: Swift version 1.2
`import Foundation // Allow for easy character checkingextension String {    subscript (i: Int) -> String {        return String(Array(self)[i])    }} func isPalindrome(str:String) -> Bool {    if (count(str) == 0 || count(str) == 1) {        return true    }    let removeRange = Range<String.Index>(start: advance(str.startIndex, 1), end: advance(str.endIndex, -1))    if (str[0] == str[count(str) - 1]) {        return isPalindrome(str.substringWithRange(removeRange))    }    return false}`
Works with: Swift version 2.0
`func isPal(str: String) -> Bool {  let c = str.characters  return lazy(c).reverse()    .startsWith(c[c.startIndex...advance(c.startIndex, c.count / 2)])}`

## Tailspin

` templates palindrome  [\$...] -> #  when <=\$(last..first:-1)> do '\$...;' !end palindrome [['rotor', 'racecar', 'level', 'rosetta']... -> palindrome ] -> !OUT::write `
Output:
```[rotor, racecar, level]
```

## Tcl

Non-recursive

`package require Tcl 8.5proc palindrome {s} {    return [expr {\$s eq [string reverse \$s]}]}`

Recursive

`proc palindrome_r {s} {    if {[string length \$s] <= 1} {        return true    } elseif {[string index \$s 0] ne [string index \$s end]} {        return false    } else {        return [palindrome_r [string range \$s 1 end-1]]    }}`

Testing

`set p ingirumimusnocteetconsumimurigniputs "'\$p' is palindrome? [palindrome \$p]"puts "'\$p' is palindrome? [palindrome_r \$p]"`

## TUSCRIPT

` \$\$ MODE TUSCRIPTpal  ="ingirumimusnocteetconsumimurigni"pal_r=TURN(pal)SELECT palCASE \$pal_rPRINT "true"DEFAULTPRINT/ERROR "untrue"ENDSELECT `
Output:
```true
```

## TypeScript

`const detectNonLetterRegexp=/[^A-ZÀ-ÞЀ-Я]/g; function stripDiacritics(phrase:string){    return phrase.normalize('NFD').replace(/[\u0300-\u036f]/g, "")} function isPalindrome(phrase:string){    const TheLetters = stripDiacritics(phrase.toLocaleUpperCase().replace(detectNonLetterRegexp, ''));    const middlePosition = TheLetters.length/2;    const leftHalf = TheLetters.substr(0, middlePosition);    const rightReverseHalf = TheLetters.substr(-middlePosition).split('').reverse().join('');    return leftHalf == rightReverseHalf;} console.log(isPalindrome('Sueño que esto no es un palíndromo'))console.log(isPalindrome('Dábale arroz a la zorra el abad!'))console.log(isPalindrome('Я иду с мечем судия')) `

## UNIX Shell

`if [[ "\${text}" == "\$(rev <<< "\${text}")" ]]; then   echo "Palindrome"else   echo "Not a palindrome"fi`

## Ursala

The algorithm is to convert to lower case, and then compare the intersection of the argument and the set of letters (declared in the standard library) with its reversal. This is done using the built in operator suffixes for intersection (c), identity (i), reversal (x) and equality (E).

`#import std palindrome = ~&cixE\letters+ * -:~& ~=`A-~rlp letters`

This test programs applies the function to each member of a list of three strings, of which only the first two are palindromes.

`#cast %bL examples = palindrome* <'abccba','foo ba rra bo of','notone'>`
Output:
`<true,true,false>`

## Vala

Checks if a word is a palindrome ignoring the case and spaces.

`bool is_palindrome (string str) {    var tmp = str.casefold ().replace (" ", "");    return tmp == tmp.reverse ();} int main (string[] args) {    print (is_palindrome (args[1]).to_string () + "\n");    return 0;}`

## VBA

This function uses function Reverse() (or Rreverse()) from Reverse a string, after first stripping spaces from the string using the built-in function Replace and converting it to lower case. It can't handle punctuation (yet). Just like the VBScript version it could also work using StrReverse.

` Public Function isPalindrome(aString as string) as Booleandim tempstring as string  tempstring = Lcase(Replace(aString, " ", ""))  isPalindrome = (tempstring = Reverse(tempstring))End Function `
Example:
```print isPalindrome("In girum imus nocte et consumimur igni")
True
```

## VBScript

#### Implementation

`function Squish( s1 )	dim sRes	sRes = vbNullString	dim i, c	for i = 1 to len( s1 )		c = lcase( mid( s1, i, 1 ))		if instr( "abcdefghijklmnopqrstuvwxyz0123456789", c ) then			sRes = sRes & c		end if	next	Squish = sResend function function isPalindrome( s1 )	dim squished	squished = Squish( s1 )	isPalindrome = ( squished = StrReverse( squished ) )end function`

#### Invocation

`wscript.echo isPalindrome( "My dog has fleas")wscript.echo isPalindrome( "Madam, I'm Adam.")wscript.echo isPalindrome( "1 on 1")wscript.echo isPalindrome( "In girum imus nocte et consumimur igni")`
Output:
```0
-1
0
-1```

## Vedit macro language

This routine checks if current line is a palindrome:

`:PALINDROME:EOL #2 = Cur_Col-2BOLfor (#1 = 0; #1 <= #2/2; #1++) {    if (CC(#1) != CC(#2-#1)) { Return(0) }}Return(1)`

Testing:

`Call("PALINDROME")if (Return_Value) {    Statline_Message("Yes")} else {    Statline_Message("No")}Return`

## Visual Basic .NET

Translation of: VBA
`Module Module1     Function IsPalindrome(p As String) As Boolean        Dim temp = p.ToLower().Replace(" ", "")        Return StrReverse(temp) = temp    End Function     Sub Main()        Console.WriteLine(IsPalindrome("In girum imus nocte et consumimur igni"))    End Sub End Module`
Output:
`True`

## Vlang

`fn is_pal(ss string) bool {    s := ss.runes()    for i in 0..s.len/2 {        if s[i] != s[s.len-1-i]{            return false        }    }    return true} fn main() {    for word in ["rotor", "rosetta", "step on no pets", "été", "wren", "🦊😀🦊"] {        println('\$word => \${is_pal(word)}')    }}`
Output:
```Are the following palindromes?
rotor => true
rosetta => false
step on no pets => true
été => true
wren => false
🦊😀🦊 => true
```

## Wortel

`@let {  ; Using a hook  pal1 @(= @rev)  ; Function with argument  pal2 &s = s @rev s  ; for inexact palindromes  pal3 ^(@(= @rev) .toLowerCase. &\@replace[&"\s+"g ""])  [[    !pal1 "abcba"    !pal2 "abcbac"    !pal3 "In girum imus nocte et consumimur igni"  ]]}`
Returns:
`[true false true]`

## Wren

`var isPal = Fn.new { |word| word == ((word.count > 0) ? word[-1..0] : "") }    System.print("Are the following palindromes?")for (word in ["rotor", "rosetta", "step on no pets", "été", "wren", "🦊😀🦊"]) {    System.print("  %(word) => %(isPal.call(word))")}`
Output:
```Are the following palindromes?
rotor => true
rosetta => false
step on no pets => true
été => true
wren => false
🦊😀🦊 => true
```

## X86 Assembly

` ; x86_84 Linux nasmsection .text isPalindrome:  mov rsi, rax  mov rdi, rax   get_end:    cmp byte [rsi], 0    je get_result    inc rsi    jmp get_end   get_result:    mov rax, 0    dec rsi     compare:      mov cl, byte [rdi]      cmp byte [rsi], cl      jne not_palindrome      cmp rsi, rdi      je palindrome      inc rdi      cmp rdi, rsi      je palindrome      dec rsi      jmp compare   not_palindrome:    mov rax, 0    ret  palindrome:    mov rax, 1    ret `

## XPL0

`include c:\cxpl\codes;          \intrinsic 'code' declarationsstring 0;                       \use zero-terminated strings func StrLen(Str);               \Return number of characters in an ASCIIZ stringchar Str;int  I;for I:= 0 to -1>>1-1 do        if Str(I) = 0 then return I; func Palindrome(S);             \Return 'true' if S is a palindromechar S;int  L, I;[L:= StrLen(S);for I:= 0 to L/2-1 do        if S(I) # S(L-1-I) then return false;return true;]; \Palindrome int Word, I;[Word:=    ["otto", "mary", "ablewasiereisawelba", "ingirumimusnocteetconsumimurigni"];for I:= 0 to 4-1 do    [Text(0, if Palindrome(Word(I)) then "yes" else "no");    CrLf(0);    ];]`
Output:
```yes
no
yes
yes
```

## Yorick

Function is_palindrome meets the task description. Function prep_palindrome demonstrates how to convert an English sentence into a form that can be tested with is_palindrome (by changing case and stripping non-alphabetical characters).

`func is_palindrome(str) {    s = strchar(str)(:-1);    return allof(s == s(::-1));} func prep_palindrome(str) {    s = strchar(strlower(str));    w = where(s >= 'a' & s <= 'z');    return strchar(s(w));}`

## zkl

`fcn pali(text){   if (text.len()<2) return(False);   text==text.reverse();}fcn pali2(text){ pali((text - " \t\n.,").toLower()) }  // or whatever punctuation is`
Output:
```pali("red rum sir is murder") //--> False
pali("red rum sir is murder" - " ") //-->True, remove spaces
pali2("In girum imus nocte et consumimur igni") //-->True
```

## Zoea

` program: palindrome   case: 1        input: abcdcba         output: true    case: 2         input: dog         output: false    case: 3         input: x         output: true    case: 4         input: abc         output: false  `