Boolean values

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

Task

Show how to represent the boolean states "true" and "false" in a language.

If other objects represent "true" or "false" in conditionals, note it.

Related tasks

•   Logical operations

8th

In 8th, any non-zero number is true, as is the specific boolean value 'true'. Everything else evaluates as 'false' (including the boolean value, 'false')

11l

11l defines a built-in data type Bool, which has two values represented by the constants 0B and 1B.

360 Assembly

The are no TRUE or FALSE constants in 360 Assembly; but an often used convention is :

FALSE    DC     X'00'
TRUE     DC     X'FF'

6502 Assembly

There are no built-in true or false constants, but the functionality can be easily replicated with zero or nonzero values (or any two values which can cause a mutually exclusive branch condition, such as with #$7f and #$80 and using BMI/BPL)

8051 Assembly

A single bit represents true or false. By convention, 0 (cleared) is false, 1 (set) is true. In the following, "bit" represents the direct address of any of the 256 directly accessible bits.

clr bit ; clears
setb bit ; sets

68000 Assembly

There are no built-in true or false constants, but the functionality can be easily replicated with zero or nonzero values (or any two values which can cause a mutually exclusive branch condition, such as with #$7f and #$80 and using BMI/BPL)

AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits

/* ARM assembly AARCH64 Raspberry PI 3B */
/*  program boolean.s   */

/*******************************************/
/* Constantes file                         */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"
.equ FALSE,  0      // or other value
.equ TRUE,   1      // or other value
/*******************************************/
/* Initialized data                        */
/*******************************************/
.data
szMessTrue:    .asciz "The value is true.\n"
szMessFalse:   .asciz "The value is false.\n"
/*******************************************/
/* UnInitialized data                      */
/*******************************************/
.bss 
/*******************************************/
/*  code section                           */
/*******************************************/
.text
.global main 
main:                            // entry of program 
 
    mov x0,0
    //mov x0,#1                  //uncomment pour other test
    cmp x0,TRUE
    bne 1f
                                 // value true
    ldr x0,qAdrszMessTrue
    bl affichageMess
    b 100f
1:   // value False
    ldr x0,qAdrszMessFalse
    bl affichageMess
 
100:                             // standard end of the program */
    mov x0,0                     // return code
    mov x8,EXIT                  // request to exit program
    svc 0                        // perform the system call
qAdrszMessTrue:         .quad szMessTrue
qAdrszMessFalse:        .quad szMessFalse
/********************************************************/
/*        File Include fonctions                        */
/********************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"

ACL2

Same as Boolean Values#Common Lisp.

Action!

PROC Test(BYTE v)
  PrintF("Variable v has value %B%E",v)
  IF v THEN
    PrintE("Condition IF v is satisfied.")
  ELSE
    PrintE("Condition IF v is not satisfied.")
  FI
  IF v=0 THEN
    PrintE("Condition IF v=0 is satisfied.")
  ELSE
    PrintE("Condition IF v=0 is not satisfied.")
  FI
  IF v<>0 THEN
    PrintE("Condition IF v<>0 is satisfied.")
  ELSE
    PrintE("Condition IF v<>0 is not satisfied.")
  FI
  IF v#0 THEN
    PrintE("Condition IF v#0 is satisfied.")
  ELSE
    PrintE("Condition IF v#0 is not satisfied.")
  FI
  PutE()
RETURN

PROC Main()
  Test(0)
  Test(1)
  Test(86)
RETURN

Output:

Screenshot from Atari 8-bit computer

Variable v has value 0
Condition IF v is not satisfied.
Condition IF v=0 is satisfied.
Condition IF v<>0 is not satisfied.
Condition IF v#0 is not satisfied.

Variable v has value 1
Condition IF v is satisfied.
Condition IF v=0 is not satisfied.
Condition IF v<>0 is satisfied.
Condition IF v#0 is satisfied.

Variable v has value 86
Condition IF v is satisfied.
Condition IF v=0 is not satisfied.
Condition IF v<>0 is satisfied.
Condition IF v#0 is satisfied.

Ada

Ada has a predefined discrete type with the specification:

   type Boolean is (False, True);

with Boolean lattice and relational operations defined on it. See RM A.1.

ALGOL 68

Translation of: python

Works with: ALGOL 68 version Standard - no extensions to language used

Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny

ALGOL 68 Enforces strong typing and so has few default coercions. The appropriate operators must be used to convert to and from bool[ean] and the following code demonstrates principle conversions:

BOOL f = FALSE, t = TRUE;
[]BOOL ft = (f, t);
STRING or = " or ";
FOR key TO UPB ft DO
  BOOL val = ft[key];
  UNION(VOID, INT) void = (val|666|EMPTY);
  REF STRING ref = (val|HEAP STRING|NIL);
  INT int = ABS val; 
  REAL real = ABS val; 
  COMPL compl = ABS val;
  BITS bits = BIN ABS val; # or bitspack(val); #
  BYTES bytes = bytes pack((val|"?"|null char)*bytes width);
  CHAR char = (val|"?"|null char);
  STRING string = (val|"?"|""); 
 
  print((((val | "TRUE" | "FALSE" ), ": ", val, or, (val|flip|flop), new line)));
  print(("  void: ", " => ", (void|(VOID):FALSE|TRUE), new line));
  print(("   ref: ", " => ", ref ISNT REF STRING(NIL), new line));
  print(("   int: ", int     , " => ", int /= 0, new line));
  print(("  real: ", real    , " => ", real /= 0, new line));
  print((" compl: ", compl   , " => ", compl /= 0, new line));
  print(("  bits: ", bits    , " => ", ABS bits /= 0, or, bits /= 2r0, or, 
                     bits width ELEM bits, or, []BOOL(bits)[bits width], new line));
  print((" bytes: """, STRING(bytes)    , """ => ", 1 ELEM bytes /= null char, or, 
                       STRING(bytes) /= null char*bytes width, or, 
                       STRING(bytes)[1] /= null char, new line));
  print(("  char: """, char  , """ => ", ABS char /= 0 , or, char /= null char, new line));
  print(("string: """, string  , """ => ", string /= "", or, UPB string /= 0, new line));
  print((new line))
OD

Output:

FALSE: F or F
  void:  => F
   ref:  => F
   int:          +0 => F
  real: +0.00000000000000e  +0 => F
 compl: +0.00000000000000e  +0+0.00000000000000e  +0 => F
  bits: FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF => F or F or F or F
 bytes: "" => F or F or F
  char: "" => F or F
string: "" => F or F

TRUE: T or T
  void:  => T
   ref:  => T
   int:          +1 => T
  real: +1.00000000000000e  +0 => T
 compl: +1.00000000000000e  +0+0.00000000000000e  +0 => T
  bits: FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFT => T or T or T or T
 bytes: "????????????????????????????????" => T or T or T
  char: "?" => T or T
string: "?" => T or T

Note: The string repr[esentation] of false and true are defined by the variables flop and flip respectively.

ALGOL W

The boolean type is called logical in Algol W - the values are represented by the keywords true and false. Numbers, strings etc. cannot be used where logical values are required.

APL

0 and 1 are used for boolean types in APL (as in J below).

    1 ^ 1
1
    1 ^ 0
0

AppleScript

AppleScript has built-in boolean keywords true and false. Numbers do not work in place of boolean expressions, but they do coerce to and from.

1 > 2     --> false 
not false --> true

{true as integer, false as integer, 1 as boolean, 0 as boolean}
          --> {1, 0, true, false}

true = 1  --> false

AppleScript also has constants yes and no, which coerce easily to boolean values. They have little practical value in AppleScript except if one wishes to use them as arguments in place of boolean values for novelty's sake. They are interchangeable with boolean values as parameters in AppleScriptObjC (not demonstrated here).

{yes as boolean, no as boolean}
          --> {true, false}

yes and no do not coerce to integer values.

Finally, AppleScript also includes keywords with and without, used in declaring parameters for and sending parameters of boolean nature to handlers. They are synonymous with true and false, respectively, and the compiler will sometimes perform the substitution at compile time.

sortItems from L given reversal : true

gets compiled immediately to become:

sortItems from L with reversal

However, the equivalent call to the handler utilising yes, whilst accepted readily in place of its boolean counterpart, is left alone by the compiler:

sortItems from L given reversal:yes

ARM Assembly

Works with: as version Raspberry Pi

/* ARM assembly Raspberry PI  */
/*  program areaString.s   */

/* Constantes    */
@ The are no TRUE or FALSE constants in ARM Assembly
.equ FALSE,  0      @ or other value
.equ TRUE,   1      @ or other value
.equ STDOUT, 1     @ Linux output console
.equ EXIT,   1     @ Linux syscall
.equ WRITE,  4     @ Linux syscall
/* Initialized data */
.data
szMessTrue: .asciz "The value is true.\n"
szMessFalse: .asciz "The value is false.\n"

/* UnInitialized data */
.bss 

/*  code section */
.text
.global main 
main:                /* entry of program  */
    push {fp,lr}    /* saves 2 registers */
 
    mov r0,#0
    //mov r0,#1   @uncomment pour other test
    cmp r0,#TRUE
    bne 1f
    @ value true
    ldr r0,iAdrszMessTrue
    bl affichageMess
    b 100f
1:   @ value False
    ldr r0,iAdrszMessFalse
    bl affichageMess
 
100:   /* standard end of the program */
    mov r0, #0                  @ return code
    pop {fp,lr}                 @restaur 2 registers
    mov r7, #EXIT              @ request to exit program
    swi 0                       @ perform the system call
iAdrszMessTrue:		.int szMessTrue
iAdrszMessFalse:		.int szMessFalse
/******************************************************************/
/*     display text with size calculation                         */ 
/******************************************************************/
/* r0 contains the address of the message */
affichageMess:
    push {fp,lr}    			/* save  registres */ 
    push {r0,r1,r2,r7}    		/* save others registers */
    mov r2,#0   				/* counter length */
1:      	/* loop length calculation */
    ldrb r1,[r0,r2]  			/* read octet start position + index */
    cmp r1,#0       			/* if 0 its over */
    addne r2,r2,#1   			/* else add 1 in the length */
    bne 1b          			/* and loop */
                                /* so here r2 contains the length of the message */
    mov r1,r0        			/* address message in r1 */
    mov r0,#STDOUT      		/* code to write to the standard output Linux */
    mov r7, #WRITE             /* code call system "write" */
    swi #0                      /* call systeme */
    pop {r0,r1,r2,r7}     		/* restaur others registers */
    pop {fp,lr}    				/* restaur des  2 registres */ 
    bx lr	        			/* return  */

Arturo

a: true
b: false

if? a [ print "yep" ] else [ print "nope" ]

if? b -> print "nope" 
else  -> print "yep"

Output:

yep
yep

AutoHotkey

When an expression is required to evaluate to true or false (such as an IF-statement), a blank or zero result is considered false and all other results are considered true. Operators such as NOT/AND/OR/>/=/< automatically produce a true or false value: they yield 1 for true and 0 for false. A variable can be used to hold a false value simply by making it blank or assigning 0 to it. The words 'true' and 'false' are built-in variables containing 1 and 0. They can be used to make a script more readable.

Avail

While Avail has many methods for handling booleans, boolean itself is simply an enumeration type of the atoms true and false. This enumeration and these atoms are only special by convention of being used for the logical operations provided by the standard library. It would be perfectly possible to define an entirely new boolean system with new types and atoms (or values).

AWK

There is no keyword for true or false in awk. In awk, any nonzero numeric value or any nonempty string value is true. Any other value (zero or the null string "") is false. Values containing only zeros may produce true or false depending on whether they are obtained from the datasource or by assignment, and different results may be obtained according to which version of awk is being used.

• Reference: AWK Truth values

In the following example we use zero for false, and one for true to assign boolean values. However, this is just a convention, so other values may also have been used:

BEGIN {
   # Do not put quotes round the numeric values, or the tests will fail
   a = 1    # True
   b = 0    # False

   # Boolean evaluations
   if (a) { print "first test a is true" }        # This should print
   if (b) { print "second test b is true" }       # This should not print
   if (!a) { print "third test a is false" }      # This should not print
   if (!b) { print "forth test b is false" }      # This should print

   # Boolean evaluation using comparison against zero
   if (a == 0) { print "fifth test a is false" }  # This should not print
   if (b == 0) { print "sixth test b is false" }  # This should print
   if (a != 0) { print "seventh test a is true" } # This should print
   if (b != 0) { print "eighth test b is true" }  # This should not print

 }

Axe

In Axe, there are no keywords for true and false. Any expression that evaluates to zero is considered false, and any expression that evaluates to non-zero is considered true. Unlike other languages, there is no canonical value for true (e.g. 1).

BASIC

Most BASICs have no keywords for true and false. Boolean expressions evaluate to 0 when false, and a non-zero value (traditional versions of basic use a value of one, although some variants use a value of negative one) when true. Numbers also work in place of boolean expressions following those rules.

10 LET A%=0
20 LET B%=NOT(A%)
30 PRINT "THIS VERSION OF BASIC USES"
40 PRINT B%; " AS ITS TRUE VALUE"
50 IF A% THEN PRINT "TEST ONE DOES NOT PRINT"
60 IF B% THEN PRINT "TEST TWO DOES PRINT"
70 IF A%=0 THEN PRINT "TEST THREE (FALSE BY COMPARISON) DOES PRINT"
80 IF B%=0 THEN PRINT "TEST FOUR (FALSE BY COMPARISON) DOES NOT PRINT"
90 IF A%<>0 THEN PRINT "TEST FIVE (TRUE BY COMPARISON) DOES NOT PRINT"
100 IF B%<>0 THEN PRINT "TEST SIX (TRUE BY COMPARISON) DOES PRINT"
110 END

Applesoft BASIC

IF statement condition treats any non-zero numeric value as true. Comparison operators evaluate to 1 (true) or 0 (false).

Examples:

? 2 = 3
? 2 = 2
IF 7 THEN ?"HELLO"

Output:

0
1
HELLO

BaCon

' Boolean TRUE and FALSE are non-zero and zero constants
a = TRUE
b = FALSE
PRINT a, ", ", b

IF 0 THEN PRINT "TRUE" : ELSE PRINT "FALSE"
IF 1 THEN PRINT "TRUE"
IF 2 THEN PRINT "TRUE"

Output:

prompt$ bacon boolean.bac
Converting 'boolean.bac'... done, 8 lines were processed in 0.004 seconds.
Compiling 'boolean.bac'... cc  -c boolean.bac.c
cc -o boolean boolean.bac.o -lbacon -lm
Done, program 'boolean' ready.
prompt$ ./boolean
1, 0
FALSE
TRUE
TRUE

BASIC256

' BASIC256 used numbers to represent true and false
' values.  Zero is false and anything else is true.
' The built in constants true and false exist
' and represent one and zero respectively.

print false
print true

BBC BASIC

      REM BBC BASIC uses integers to represent Booleans; the keywords
      REM FALSE and TRUE equate to 0 and -1 (&FFFFFFFF) respectively:
      
      PRINT FALSE
      PRINT TRUE

Cherrycake

The boolean value of true in Cherrycake is represented with a 'true' keyword, and the boolean value of false in Cherrycake is represented with a 'false' keyword. Booleans can also be represented with other types, such as binary and integers. In binary types, 0x01 and 0b01 represent true, and 0x00 and 0b00 represent false. In integer types, 1 represents true and 0 represents false.

Commodore BASIC

Commodore BASIC evaluates any non-zero number for TRUE—but is typically represented as 16-bit signed integer value of -1 or $FFFF—and zero evaluates to FALSE.

10 f%=("z"="a") : t%=not f% : rem capture a boolean evaluation
15 print chr$(147);chr$(14);
20 print "True is evaulated as:";t%
30 print "False is evaluated as:";f%
40 print:print "Any non-zero number will evaluate to"
50 print "true as shown in this example:":print
60 for i=-2 to 2
70 print i;" = ";
80 if i then print "True":goto 100
90 print "False"
100 next

Output:

True is evaulated as:-1                 
False is evaluated as: 0                
                                        
Any non-zero number will evaluate to    
true as shown in this example:          
                                        
-2  = True                              
-1  = True                              
 0  = False                             
 1  = True                              
 2  = True                              
                                        
ready.
█

FreeBASIC

FreeBASIC has a built-in Boolean type (equivalent to a signed one byte integer) with built-in constants true and false to represent values of that type. Note also that:

• Numeric expresions can be converted to the Boolean type either implicitly or using the CBool operator - zero is converted to false and non-zero to true.

• Boolean expressions can be converted to a numeric type either implicitly or using the appropriate cast operator (CInt, CByte, CDbl etc) - false is converted to 0 and true to -1.

• String expressions such as "false" and "true" (regardless of case) can also be converted to Boolean using CBool.

• It is possible to overload CBool for user-defined types to yield a Boolean value.

Sample code:

' FB 1.05.0 Win64

Dim i As Integer = 23
Dim s As String = "False"
Dim b As Boolean
b = i
Print b
b = CBool(s)
Print b
i = b
Print i
i = CInt(true)
Print i
Sleep

Output:

true
false
 0
-1

Liberty BASIC

IF-statement, loop condition treats any non-zero integer as true. Comparison operators evaluate to 1 (true) or 0 (false).

Microsoft Small Basic

Microsoft Small Basic has two constants: "True" and "False".

If c Then
  notc = "False"
Else
  notc = "True"
EndIf

PowerBASIC

In addition to what's noted above under BASIC, PowerBASIC for Windows and PowerBASIC Console Compiler have the ISTRUE and ISFALSE functions. According to the help file, they "return the logical truth or falsity of a given expression". (PowerBASIC lacks a boolean data type, so the usual practice is to use integers in PB/DOS, and longs in PB/CC and PB/Win.)

DIM x AS LONG
x = ISTRUE(1 = 1)  ' returns -1
x = ISTRUE(1 = 0)  ' returns 0
x = ISFALSE(1 = 1) ' returns 0
x = ISFALSE(1 = 0) ' returns -1

PureBasic

PureBasic does not have a Boolean variable type. An integer type is typically used instead. Boolean values are only supported as part of a loop's condition (While/Wend, Repeat/Until) or in a conditional (If/Endif). In these cases if the result of a variable or a numeric expression is zero it is evaluated as False, otherwise it is evaluated as True. A string variable assigned a null string would be evaluated as False.

QBasic

QBasic, QuickBASIC, VB-DOS and GW-BASIC doesn't have a Boolean type. What it does is to take 0 as False, and any other value as True. The easiest way in QBASIC, QuickBASIC and VB-DOS is to create False and True constants of type Integer and, then, use them as needed:

CONST FALSE=0
CONST TRUE = Not FALSE
Print FALSE
Print TRUE

In GW-BASIC you can create a variable called FALSE% and other called TRUE% and do the same. Nevertheless, is more sure to create functions in order to avoid the value to be manipulated:

10 DEF FNFALSE = 0
20 DEF FNTRUE = NOT FNFALSE
30 Print FNFALSE
40 Print NFTRUE

Run BASIC

Basically 0 is false and 1 is true

if 1          then print "1 is true"
if not(0)     then print "0 is false" 
if 1 < 2      then print "1 < 2 TRUE"
if 2 > 1      then print "2 > 1 TRUE"
if not(2 < 1) then print "2 not < 1"
if not(1 = 0) then print "1 not = 0"

SmallBASIC

a = true
b = false

smart BASIC

• IF/THEN statements treat any non-zero value as true and zero as false.
• Comparison operators DO NOT calculate in smart BASIC. For example, PRINT (1 > 4) WILL NOT evaluate to produce a zero value (0) indicating a false condition. It will produce an error. All Boolean evaluations in smart BASIC must be determined within IF/THEN statements.

TI-89 BASIC

There are boolean literals true and false. No other values may be used where a boolean is expected.

True BASIC

!True BASIC maneja correctamente las expresiones booleanas,
!Pero no tiene un tipo booleano. 

!La solución: crear constantes False y True y usarlas según sea necesario."
LET False = 0
LET True =  1
PRINT True; ", "; False

IF True = 0 THEN PRINT "TRUE" ELSE PRINT "FALSE"
IF True > False THEN PRINT "TRUE" ELSE PRINT "FALSE"

!Para el operador NOT, los paréntesis rodean la cláusula completa.
IF Not(2 < 1) then PRINT "TRUE" ELSE PRINT "FALSE"

END

Output:

1 ,  0
FALSE
TRUE
TRUE

uBasic/4tH

In conditionals, zero is false, non-zero is true. Note that = is not only used for assignment, it is also a fully qualified logical operator, so it is easy to assign a true boolean to a variable.

t = 1 = 1
f = 0 = 1

Print "False = ";f;", True = ";t

Output:

False = 0, True = 1

0 OK, 0:52

Yabasic

// Yabasic usa números para representar los valores true y false
// Las constantes incorporadas true y false representan uno y cero respectivamente.

//false también puede escribirse como FALSE o incluso FaLsE.
//true también puede escribirse como TRUE o incluso TrUe.

print false
print true
end

Visual Basic

VB has the Boolean data type and the constants True and False, in addition to what's listed under BASIC, above. When used outside of a boolean context, True and False return values depending on their context -- -1 and 0 in a numeric context, "True" and "False" if used as strings.
When converting an integer to a boolean, 0 is False and anything not equal to 0 is

Dim x As Boolean
x = IIf(Int(Rnd * 2), True, False)
MsgBox x

Batch File

The closest thing to Boolean values in batch files is using if defined. If a variable has any value, it will evaluate to true.

You can make a variable false by clearing its value set "var=".

@echo off

::true
set "a=x"
::false
set "b="

if defined a (
	echo a is true
) else (
	echo a is false
)
if defined b (
	echo b is true
) else (
	echo b is false
)

pause>nul

Output:

a is true
b is false

bc

POSIX bc doesn't define Boolean values (i.e. it's up to the programmer which values represent false and true).

In GNU bc, 0 is false and any other value is true (but the result of a boolean expression will always be 1 if it is true).

Befunge

Zero is false, non-zero is true. This is only used by the horizontal and vertical switch operators (_ and |).

Binary Lambda Calculus

The standard representations for the booleans in lambda calculus are true = \then. \else. then, false = \then. \else. else, which correspond to BLC programs 00 00 110 and 00 00 10.

BQN

For predicates, the boolean value given must be 0 or 1. All other values error.

{1?34}
  34
{⟨⟩?34}
  ERROR

For logical assertion, the test is simply whether the right argument is 1 (𝕩≡1). Anything other than 1 will cause an error.

!1
  1
!⟨⟩
  ERROR
!0
  ERROR

Bracmat

Bracmat operates with success and failure instead of true and false. Success and failure play the same role as true and false in conditional tests, but they are not values like true and false. Instead, success and failure are properties of expressions in addition to values. The simplest failing expression is the atomic expression ~. The simplest succeeding atomic expression is the empty string "" (or ()). A slightly more complex failing expression is 1+1:3, which postulates that 3 matches the result of adding 1 and 1, while 1+1:2 of course succeeds.

Brainf***

Zero is false, non-zero is true. This is only used by the loop brackets ([ and ]).

C

In C, a value which is equal to 0 is false, while a value which is not equal to 0 is true. Relational and logical operators evaluate to 0 for false and 1 for true. Any of the following can be used:

• any integer type, where 0 gives false, and any other value gives true (note that in C, character types are also integer types, therefore this also applies to characters: the '\0' character is false)
• any floating point type, where again, 0 gives false and everything else gives true
• any enumeration type, again 0 gives false, anything else true
• any pointer type, where the null pointer gives false and any other pointer gives true
• in C99, the boolean type bool (defined in header <stdbool.h>), where true gives true and false gives false
• in C99, any complex number type, where 0 (0 real and 0 imaginary) gives false, anything else gives true

C#

In C#, there are the reserved keywords true and false. Variables to hold these values are declared as either bool or Boolean. These types are identical, as bool is just shorthand for Boolean. The collection type BitArray returns its values as Boolean, packing 8 values into each byte (In contrast, the Boolean type uses the entire byte for one value).

There is also the Nullable<T> type that represents all values of its underlying value type T and an additional null value. It has a shorthand notation: T? (When T is a reference type, T? means something else. It is not a different type, but just a hint to the compiler.) So, when applied to bool, we have a bool? type that supports 3 values: true, false and null. This can be useful for some applications where the value can be undefined or missing.

bool? value = null

Unlike C/C++, there is no conversion in C# between other types and Boolean.

C++

In C++, there are the constants true and false to represent those values. However, there are numerous implicit conversions to bool, therefore in conditions (and other contexts expecting boolean values), any of the following can be used:

• any integer type, where 0 converts to false, and any other value converts to true (note that in C++, character types are also integer types, therefore this also applies to characters: the '\0' character is false)
• any floating point type, where again, 0 gives false and everything else gives true
• any enumeration type, again 0 gives false, anything else true
• any pointer type, where the null pointer gives false and any other pointer gives true
• any user-defined type with an implicit conversion operator either to bool or to a built-in type which itself can be converted to bool (i.e. any of the above). The C++ standard library contains one such implicit conversion: the implicit conversion of a stream s to bool gives !s.fail()

Clean

The standard library defines a data type Bool, which has exactly two members:

::Bool = False | True

In addition to all the functionality of any other Clean algebraic data type (e.g. pattern matching), and the specified derived typeclass instances, the built-in guard (“|”) and if syntaxes use Bool.

As with any other Clean data type, there are no automatic conversions of other types to Bool.

Clojure

The boolean constants are true and false. In a conditional context, the only false values are false and nil -- every other value is true.

CMake

foreach(var 1 42 ON yes True y Princess
            0 OFF no False n Princess-NOTFOUND)
  if(var)
    message(STATUS "${var} is true.")
  else()
    message(STATUS "${var} is false.")
  endif()
endforeach(var)

-- 1 is true.
-- 42 is true.
-- ON is true.
-- yes is true.
-- True is true.
-- y is true.
-- Princess is true.
-- 0 is false.
-- OFF is false.
-- no is false.
-- False is false.
-- n is false.
-- Princess-NOTFOUND is false.

The strings "0", "OFF", "NO", "FALSE" and "N" (ignoring case) are false. Any string ending with "-NOTFOUND" (ignoring case) is false. All other strings are true.

Scripts that want if(TRUE) should require CMake 2.8; do refer to cmake --help-policy CMP0012.

COBOL

Booleans

Booleans are defined as any data item having a PICTURE made up of ones.

       01  some-bool               PIC 1 BIT.

The boolean literals B"1" and B"0" represent true and false, respectively.

Conditions

Prior to COBOL 2002, there was no boolean data type, only condition names which could be used in conditional expressions. Condition names are subordinate to another data item, have the level-number 88, and are defined with the value(s) which their parent data item must have for them to be set to true. They can be defined like so:

       01  X PIC 9.
           88 X-Is-One        VALUE 1.
           88 X-Is-Even       VALUE 0 2 4 6 8.
           88 X-Larger-Than-5 VALUE 6 THRU 9.

Conditions can be SET to TRUE or FALSE. Setting a condition to TRUE will move the (first) value in the VALUE clause to the parent data item. In COBOL 2002, an optional FALSE clause was added which allowed the condition to be SET to FALSE and consequently set the parent data item to the specified value in the clause. A FALSE clause can only have one value. An example of conditions in action:

       PROGRAM-ID. Condition-Example.

       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01  Foo PIC 9 VALUE 5.
           88  Is-Not-Zero VALUE 1 THRU 9
               WHEN SET TO FALSE IS 0.

       PROCEDURE DIVISION.
       Main.
           PERFORM Is-Foo-Zero

           SET Is-Not-Zero TO FALSE
           PERFORM Is-Foo-Zero

           SET Is-Not-Zero TO TRUE
           PERFORM Is-Foo-Zero

           GOBACK
           .

       Is-Foo-Zero.
           IF Is-Not-Zero
               DISPLAY "Foo is not zero, it is " Foo "."
           ELSE
               DISPLAY "Foo is zero."
           END-IF
           .

Output:

Foo is not zero, it is 5.
Foo is zero.
Foo is not zero, it is 1.

CoffeeScript

CoffeeScript is largely based on JavaScript, but that may only serve to confuse you. Your best bet is to learn all the cases:

h1 = {foo: "bar"}
h2 = {foo: "bar"}

true_expressions = [
  true
  1
  h1? # because h1 is defined above
  not false
  !false
  []
  {}
  1 + 1 == 2
  1 == 1 # simple value equality
  true or false
]

false_expressions = [
  false
  not true
  undeclared_variable?
  0
  ''
  null
  undefined
  h1 == h2 # despite having same key/values
  1 == "1" # different types
  false and true
]

Common Lisp

The only value in Common Lisp that is false is the symbol nil; all other values are true. The symbol t is the canonical true value.

Considered as variables, nil and t are bound to themselves ("self-evaluating"). nil, as well as being false, is used as the empty list; i.e. an empty list is false.

For more information, follow the links from CLHS: Type BOOLEAN.

Component Pascal

VAR
   b,c: BOOLEAN;
...
   b := TRUE;
   c := FALSE;
...

Crystal

Crystal uses the "truthiness" of a value to determine whether or not to execute the body of an if, unless, while, or until block.

As mentioned in the language reference, the values nil and false, as well as null pointers are "falsey", all other values are truthy

if false
  puts "false"
elsif nil
  puts "nil"
elsif Pointer(Nil).new 0
  puts "null pointer"
elsif true && "any other value"
  puts "finally true!"
end

D

In D, there are constants false and true to represent their respective values (that also implicitly convert to 0 and 1). Implicit conversions to boolean are listed below:

• Any integer type, where 0 converts to false, and any other value converts to true;
• Any floating point type, where again, 0 gives false and everything else (but NaNs) gives true;
• Any enumeration type, again 0 gives false, anything else true;
• Any pointer type, where the null pointer gives false and any other pointer gives true;
• Any class reference type, using the "is" operator, the null reference gives false and any other reference gives true;
• Any user-defined type with an implicit conversion operator (opCast) either to bool or to a built-in type which itself can be converted to bool.

Dc

In dc there are no built in boolean values or functions. Adopting the way C codes them appears to be a good idea: 0=FALSE and 1=TRUE.

Delphi

In addition to the types defined by Object Pascal, Delphi defines the type Bool.

DWScript

The standard Boolean type has two values: True and False, with Ord(False) = 0 and Ord(True) = 1.

Dyalect

Dyalect has a standard Bool type with two values: true and false. Other types in Dyalect support implicit conversion to booleans. All values except false and nil are converted to true.

Dylan

#t // <boolean> true
#f // <boolean> false

For the purpose of conditional statements, all objects other than #f evaluate to true.

Déjà Vu

Déjà Vu has true and false, two numbers that are equal to 1 and 0 respectively. Every object has a truth value. The only falsy things are numbers equal to zero, empty lists and dictionaries, and zero-length strings and blobs.

E

E defines two basic objects true and false, and the boolean guard which accepts them. All builtin operations which take booleans (e.g. the if control structure) coerce the input to boolean.

? if (true) { "a" } else { "b" }
# value: "a"

? if (false) { "a" } else { "b" }
# value: "b"

? if (90) { "a" } else { "b" }
# problem: the int 90 doesn't coerce to a boolean

No objects in the standard library coerce to boolean, but user-written objects may choose to do so; they can then be used in place of booleans.

? def bowlian {
>     to __conformTo(guard) {
>         if (guard == boolean) { return true }
>     }
> }
> if (bowlian) { "a" } else { "b" }
# value: "a"

EasyLang

EasyLang does not have built-in boolean types or constants. Operators that "return" a boolean type (e.g. >, <=) cannot be used outside of conditional statements and loops.

You can use 1 or 0 in place of true and false.

boolNumber = 1
if boolNumber = 1
   print "True"
else
   print "False"
.

EchoLisp

"All that which is not false is true" - Attribué à L. Wittgenstein - The only false value is the boolean #f. All other objects, including the empty list or null or 0 ..- evaluate to #t = true.

(not #t)  → #f
(not #f)  → #t
(not null) → #f
(not 0) → #f

Ecstasy

Ecstasy's defines an enumeration named Boolean, which contains the values  False  and  True .

module GeorgeBoole {
    @Inject Console console;

    void run() {
        Boolean f = False;
        assert !f == True;

        // methods like "and", "or", "xor", and "not" are the same as
        // the operators "&"/"&&", "|"/"||", "^"/"^^", and the unary "~"
        assert True.and(False) == True & False == False;
        assert True.or(False)  == True | False == True;
        assert True.xor(False) == True ^ False == True;
        assert True.not() == ~True == False;

        console.print($"0==1 = {0==1}");
        console.print($"!False = {!False}");
    }
}

Output:

0==1 = False
!False = True

EGL

In EGL boolean is a primitive type, however it acts the same as an integer (type int). A boolean and an int accept integer values aswel as true and false keywords (which represent resp. 1 and 0). A boolean is always true except when it has value 0 (or keyword false). A boolean can be converted to a string ("true" or "false") using StrLib.booleanAsString(boolean);

myBool boolean = 0;
SysLib.writeStdout("myBool: " + StrLib.booleanAsString(myBool));
myBool = 1;
SysLib.writeStdout("myBool: " + StrLib.booleanAsString(myBool));
myBool = 2;
SysLib.writeStdout("myBool: " + StrLib.booleanAsString(myBool));
myBool = false;
SysLib.writeStdout("myBool: " + StrLib.booleanAsString(myBool));
myBool = true;
SysLib.writeStdout("myBool: " + StrLib.booleanAsString(myBool));
myInt int = 0;
SysLib.writeStdout("myInt: " + StrLib.booleanAsString(myInt));
myInt = 1;
SysLib.writeStdout("myInt: " + StrLib.booleanAsString(myInt));
myInt = 2;
SysLib.writeStdout("myInt: " + StrLib.booleanAsString(myInt));
myInt = false;
SysLib.writeStdout("myInt: " + StrLib.booleanAsString(myInt));
myInt = true;
SysLib.writeStdout("myInt: " + StrLib.booleanAsString(myInt));

Output:

myBool: false
myBool: true
myBool: true
myBool: false
myBool: true
myInt: false
myInt: true
myInt: true
myInt: false
myInt: true

Elena

ELENA uses the system'BaseBoolValue class, which has two singleton sub-classes: system'true and system'false. E.g. an expression like 5 == 5 returns system'true. There is a Boolean variable : system'Boolean.

Elixir

Elixir utilizes Erlang's definition of boolean types; they're defined as the atoms :true and :false. No other type is equal to true or false.

iex(1)> true === :true
true
iex(2)> false === :false
true
iex(3)> true === 1
false

nil (also defined as an atom, :nil) is not equal to false.

iex(4)> nil === :nil
true
iex(5)> nil === false
false

Elm

--True and False directly represent Boolean values in Elm
--For eg to show yes for true and no for false
if True then "yes" else "no"

--Same expression differently
if False then "no" else "yes"

--This you can run as a program
--Elm allows you to take anything you want for representation
--In the program we take T for true F for false
import Html exposing(text,div,Html)
import Html.Attributes exposing(style)

type Expr = T | F | And Expr Expr | Or Expr Expr | Not Expr

evaluate : Expr->Bool
evaluate expression =
 case expression of
 T ->
  True

 F ->
  False

 And expr1 expr2 ->
  evaluate expr1 && evaluate expr2

 Or expr1 expr2 ->
  evaluate expr1 || evaluate expr2

 Not expr ->
  not (evaluate expr)

--CHECKING RANDOM LOGICAL EXPRESSIONS
ex1= Not F
ex2= And T F
ex3= And (Not(Or T F)) T

main =
    div [] (List.map display  [ex1, ex2, ex3])

display expr=
   div [] [ text ( toString expr ++ "-->" ++ toString(evaluate expr) ) ]
--END

Emacs Lisp

Symbol nil is false and symbol t is true. Both are self-evaluating, being variables whose value is their own symbol. See the elisp manual for more.

In an if and similar, nil is false and anything else is true. To make that clear docstrings etc say "non-nil" for true. (See last item in elisp manual documentation tips.)

EMal

^|EMal has a dedicated Logical type expressed by the logic keyword.
 |It's not nullable and holds the two values false and true.
 |There are no implicit conversions, but explicit conversions 
 |from/to int (0,1) or text ("⊥", "⊤") are allowed.
 |^
logic booleanTrue = true
logic booleanFalse = false
if 2 > 1 and true and not false
  writeLine("true: " + true + ", false: " + false)
end
if false == logic!0
  writeLine("explicit conversion from integer")
end
if true == logic!"⊤"
  writeLine("explicit conversion from text")
end
writeLine(int!true) # is one
writeLine(text!false) # is "⊥"

Output:

true: ⊤, false: ⊥
explicit conversion from integer
explicit conversion from text
1
⊥

Erlang

Erlang doesn't technically define boolean types. Instead, the atoms true and false are used. However, they are integrated well enough into the language there should be no problem with that as long as you don't expect false and true to mean anything but literal false and true.

1> 1 < 2.
true
2> 1 < 1.
false
3> 0 == false.
false

Excel

The Logical category of functions includes the constants TRUE() and FALSE() which are displayed without the parantheses in cells. There are logical functions such as AND and OR too. For an AND truth table of two variables, take 3 cells, say A1,B1 and C1. In C1 type in :

=AND(A1;B1)

Copy this until C4. Now as values are filled in from A1-A4 and B1-B4, C1-C4 gets updated.

0	0	FALSE
0	1	FALSE
1	0	FALSE
1	1	TRUE

F#

The type bool is an abbreviation for the .NET framework type System.Boolean.

type bool = System.Boolean

Instances of this type have values of either true or false.

Factor

In Factor any value except f is true, with t being the canonical true value.

FALSE

Zero is false and non-zero is true. This is used by the if and while operators (? and #). Comparators (= and <) yield -1 for true and 0 for false.

Fantom

Conditional statements must return a sys::Bool, and the only two values are true and false.

Forth

In conditionals, zero is false, non-zero is true. There are predefined constants for the canonical forms. For FORTH-83 or later, FALSE is zero and TRUE is -1 (all bits set). For earlier FORTH standards, FALSE is zero and TRUE is 1.

TRUE .    \ -1
FALSE .   \ 0

Fortran

Fortran started off in 1957 with only floating-point and fixed-point variables, so any calculations in the style of Boolean arithmetic would be done with integer values such as zero and not-zero, using multiplication and addition for and and or.

Fortran 66 introduced a logical data type which can be set to either .true. or .false. or be generated via logical expressions such as <=, etc. Such variables cannot be used in normal arithmetic with operators such as +-*/ but only with logical operators such as .OR. and so on. If via the EQUIVALENCE statement their numerical values (or, bit patterns) are inspected as say an integer, the values may well not be as anticipated and differ between computers and compilers. For instance, on the Burroughs 6700 an integer variable equivalenced to a logical variable would appear as .true. if odd, .false. if even.

The default storage size of a LOGICAL variable is the same as the default storage size of an INTEGER variable, which for many systems is 32 bits. This is done to simplify calculations of record sizes, or the alignment of variables in COMMON storage areas. It is usually possible to declare variables with certain byte sizes (normally only powers of two) so that LOGICAL*1 or similar declarations may be available. If used however there may arise alignment issues with adjacent variables of other types (such as REAL) that may require padding to even word boundaries for best access. Consider

      TYPE MIXED
       LOGICAL*1 LIVE
       REAL*8    VALUE
      END TYPE MIXED
      TYPE(MIXED) STUFF(100)

The array STUFF might occupy 900 bytes, or, 1600 bytes if each double-precision value has to be aligned to an eight-byte boundary. In the latter case, it may be better to declare LIVE and VALUE to be separate hundred-element arrays as in

      TYPE MIXED
       LOGICAL*1 LIVE(100)
       REAL*8    VALUE(100)
      END TYPE MIXED
      TYPE(MIXED) STUFF

Except that now only hundred-element variables of type MIXED can be declared. Either way, the record size needed for a disc file holding such items will need careful thought.

Free Pascal

In addition to the types defined by Object Pascal, free Pascal defines the qWordBool, that has a sizeOf eight.
Furthermore, True and False are not keywords from FPC v3.0.0. It is possible to assign any value to true and false, like strings but even objects.

{$mode objfpc}{$ifdef mswindows}{$apptype console}{$endif}
const
  true = 'true';
  false = 'false';
begin
  writeln(true);
  writeln(false);
end.

[ EDIT ]

See https://wiki.freepascal.org/Boolean

While you can assign values to true and false, it has now nothing to do with the boolean values....
Try with this function:

FUNCTION IsNatural ( CONST num: VARIANT ): BOOLEAN;

    BEGIN

	IsNatural := ( num > 0 );

    END;

JPD 2022/08/02

Frink

The literal boolean values are called true and false. In addition, in conditional expressions, the following are treated as true:

• Any non-empty string
• Any list, even an empty list

The following are treated as false:

• The empty string
• The special value undef

Futhark

Futhark has a bool type, with the two values True and False. They are used for branching.

FutureBasic

FB recognizes two types for boolean truth values: BOOL and boolean. There is a subtle difference between the two. A BOOL will accept without complaint the macros YES, and NO, the equivalent native FB constants, _true, and _false, and, of course, 0 and 1. However, although a BOOL can be assigned other values, it will throw a clang (FB"s native compiler) warning as with this example:

window 1
BOOL boolTest
boolTest = -1
print boolTest
HandleEvents

When compiled this code generates this warning:

implicit conversion from constant value -1 to 'BOOL'; the only well defined values for 'BOOL' are YES and NO [-Wobjc-bool-constant-conversion]

On the other hand, a Boolean can be assigned not only YES, NO, _true, or _false, and 0 or 1, but also other values, such as the common -1, and compile without complaint.

Since FB can also work with objects, native BOOLs and booleans need to be converted to objects as demonstrated in the code below.

Trivia: Because NULL and _nil zero values in FB, they evaluate to "NO" or “_false” in conditional expressions.

void local fn BooleanExercise
  BOOL areEqual    = (1 == 1)      // areEqual is YES
  BOOL areNotEqual = not areEqual  /* areNotEqual is converted to: areEqual = (-(1 == 1)). -1 throws a clang warning.
  NOTE: FB does not accept the "!" shorthand for "not", i.e. !areEqual, common in other languages. */
  
  print "areEqual    == "; areEqual
  print "areNotEqual == "; areNotEqual
  print
  
  // Boolean types assigned values outside YES or NO compile without complaint.
  boolean minusOneTest = -1
  print "minusOneTest == "; minusOneTest
  
  // Typical boolean value is use
  BOOL flatterRosettaReader = YES
  if (flatterRosettaReader)
    print
    print @"Rosetta Code programmers understand booleans."
    print
  end if
  
  // Defined Core Foundation boolean values
  print "kCFBooleanTrue  == "; kCFBooleanTrue
  print "kCFBooleanFalse == "; kCFBooleanFalse
  print
  
  // Number object assigned literal value
  CFNumberRef booleanObject = @(YES)
  print "booleanObject == "; booleanObject
  print
  
  // Number object created programmatically
  booleanObject = NO
  print "booleanObject variable reassigned as N0 == "; fn NumberWithBool( booleanObject )
  print
end fn

window 1

fn BooleanExercise

HandleEvents

Output:

areEqual    == 1
areNotEqual == 0

minusOneTest == -1

Rosetta Code programmers understand booleans.

kCFBooleanTrue  == 1
kCFBooleanFalse == 0

booleanObject == 1

booleanObject variable reassigned as N0 == 0

Gambas

Click this link to run this code

Public Sub Main()
Dim bX As Boolean

Print bX
bX = True
Print bX

End

Output:

False
True

GAP

1 < 2;
# true 

2 < 1;
# false

# GAP has also the value fail, which cannot be used as a boolean but may be used i$

1 = fail;
# false

fail = fail;
# true

Go

Go defines a built-in data type bool, which has exactly two values, represented by the keywords true and false. There is no conversion between booleans and other data types. Conditionals require a boolean value, so if i is a numeric type, for example, you must spell out if i != 0 { if you wish to interpret it as boolean.

The template package however, uses a different rule for if actions. There, it is testing if a "pipeline" is "empty" where the empty values are false, 0, any nil pointer or interface value, and any array, slice, map, or string of length zero.

 
package main

import (
	"fmt"
	"reflect"
	"strconv"
)

func main() {
	var n bool = true
	fmt.Println(n)        // prt true
	fmt.Printf("%T\n", n) // prt bool
	n = !n
	fmt.Println(n) // prt false

	x := 5
	y := 8
	fmt.Println("x == y:", x == y) // prt x == y: false
	fmt.Println("x < y:", x < y)   // prt x < y: true

	fmt.Println("\nConvert String into Boolean Data type\n")
	str1 := "japan"
	fmt.Println("Before :", reflect.TypeOf(str1)) // prt Before : string
	bolStr, _ := strconv.ParseBool(str1)
	fmt.Println("After :", reflect.TypeOf(bolStr)) // prt After : bool
}

Groovy

Groovy has a boolean "primitive" type and a Boolean "object wrapper" type directly derived from Java. See the Java solution to this task for more details.

Unlike Java, any null reference converts to a boolean "false", while any non-null object reference converts to a boolean "true"... EXCEPT if that object has a specific defined conversion to boolean "false". For example, for any numeric type, any zero value representation converts to "false" and any non-zero value converts to "true". For any collection type, non-empty converts to "true" and empty converts to "false".

Haskell

The Haskell standard Prelude defines a data type Bool, which has exactly two members:

data Bool = False | True    deriving (Eq, Ord, Enum, Read, Show, Bounded)

In addition to all the functionality of any other Haskell algebraic data type (e.g. pattern matching), and the specified derived typeclass instances (e.g. False == False, succ False == True, (maxBound :: Bool) == True, etc.), the built-in guard (“|”) and if syntaxes use Bool.

As with any other Haskell data type, there are no automatic conversions of other types to Bool.

HicEst

Zero is false, non-zero is true. Numbers also work in place of boolean expressions following this rule.

HolyC

In HolyC, there are the reserved keywords `TRUE` and `FALSE`. Variables to hold these values are declared as `Bool`.

Any value which is equal to 0 is false, while a value which is not equal to 0 is true. Relational and logical operators evaluate to 0 for false and 1 for true. Any of the following can be used:

• Any integer type, where 0 gives false, and any other value gives true.
• Any floating point type, where again, 0 gives false and everything else gives true.
• Any pointer type, where the null pointer gives false and any other pointer gives true.

i

Any non-zero number is true in 'i'.

main
	//Bits aka Booleans.
	b $= bit()

	b $= true
	print(b)

	b $= false
	print(b)
	
	//Non-zero values are true.
	b $= bit(1)
	print(b)

	b $= -1
	print(b)

	//Zero values are false
	b $= 0
	print(b)
}

Icon and Unicon

Icon and Unicon do not use Boolean values for flow control. Rather they use success (returning a result, any result even a null) or failure (a signal) for this purpose. Built-in controls support not, and (&), and or (|). For an example of how this works, see Short Circuit Evaluation. Icon and Unicon do support bit operations on integers which could be used to record Boolean state. See also Logical Operations for an example of how and when Boolean values might be implemented.

Idris

Idris> :doc Bool
Data type Prelude.Bool.Bool : Type
    Boolean Data Type

Constructors:
    False : Bool


    True : Bool

Inform 6

Inform 6 has the constants true and false, which are identical to 1 and 0 respectively. One of these values will always be yielded by a condition operator (an operator that yields a boolean value). In addition, any non-zero value is considered to be true.

Inform 7

The Boolean type is called "truth state" and has the values "true" and "false".

However, Inform 7 distinguishes between Boolean values and conditions. Comparison expressions do not return truth states, and truth state expressions cannot be used directly in conditional statements. There is a conversion from condition to truth state:

let B be whether or not 123 is greater than 100;

And truth states can be used in conditions by adding an explicit comparison:

if B is true, say "123 is greater than 100."

Phrases (functions) cannot be defined to return a truth state directly. Instead, they are defined using "to decide whether" (or "to decide if") and can then be used as conditions:

To decide whether the CPU is working correctly:
	if 123 is greater than 100, decide yes;
	otherwise decide no.

When play begins:
	[convert to truth state...]
	let B be whether or not the CPU is working correctly;
	[...or use as a condition]
	if the CPU is working correctly, say "Whew."

Insitux

Simply true and false, however, anything which is not false or null is considered truthy.

J

False is 0, true is 1. This is an advantage (search for Maple).

This approach also works well with Bayes' theorem, as false matches 0% probability and true matches 100% probability.

Java

In Java, true and false are used to reference a boolean value.
There is no use of 0 and 1, or undefined vs. defined.

As with the other primitive data-types, boolean has a wrapper class, Boolean, which includes a set of valuable boolean operations.

boolean valueA = true;
boolean valueB = false;

Or.

Boolean valueA = Boolean.TRUE;
Boolean valueB = Boolean.FALSE;

Additionally.

Boolean valueA = Boolean.valueOf(true);
Boolean valueB = Boolean.valueOf(false);

JavaScript

The Boolean type has two values: true and false

The following table shows the result of type conversions to boolean:

• Undefined: any undefined value is converted to false
• Null: false
• Number: the numbers 0, -0, NaN are false; otherwise true
• String: the empty (zero-length) string is false; otherwise true
• Object: any object is converted to true

(source: ECMAScript Language Reference)

Joy

The truth literals are true and false. In a conditional context, false, numerical values (including characters) of zero, empty lists and empty sets are evaluated as false.

jq

true and false are the only entities of type "boolean":

$ jq type
true
"boolean"
false
"boolean"

The above shows the jq command invocation, followed by alternating lines of input and output.

jq's logical operators, however, do not require boolean inputs. In brief, false and null are both regarded as false, and all other JSON entities are regarded as true. That is, all values except for false and null are truthy.

Julia

Julia has a built-in Bool type with values true and false.

Other objects do not represent boolean values and cannot be used in conditional expressions, for example:

julia> if 1
         println("true")
       end
ERROR: type: non-boolean (Int64) used in boolean context

However, integers can be converted to boolean types with the bool() function (which treats nonzero values as true)

julia> bool(-2:2)
5-element Bool Array:
  true
  true
 false
  true
  true

KonsolScript

The Boolean type has two values: true and false

The following table shows the result of type conversions to boolean:

• Number: the number 0 is false; otherwise true
• String: the empty (zero-length) string is false; otherwise true

`

Kotlin

Booleans in Kotlin are given by the literals true and false, case sensitive, which are the only instances of the class Boolean.

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.

Lambdatalk

Predefined constants are true and false:

{if true then YES else NO}
-> YES
{if false then YES else NO}
-> NO

Following the lambda calculus user defined booleans can be built

{def TRUE {lambda {:a :b} :a}} 
-> TRUE
{def FALSE {lambda {:a :b} :b}}
-> FALSE
{def IF {lambda {:c :a :b}  {:c :a :b}}}
-> IF

{IF TRUE yes no}
-> yes
{IF FALSE yes no}
-> no

Lasso

Comparisons are evaluated in Lasso as either true of false, so "1 == 2" will evaluate as true, and "1 == 1" will evaluate as true.

A variable can also be assigned a boolean type, and as such then holds either true of false states.

!true
// => false

not false
// => true

var(x = true)
$x // => true

$x = false
$x // => false

In a conditional, if the result is the integer 0, it is also evaluated as boolean false. If the conditional results in an integer greater than zero, it is evaluated as boolean true.

local(x = string)
// size is 0
#x->size ? 'yes' | 'no'

local(x = '123fsfsd')
// size is 8
#x->size ? 'yes' | 'no'

Output:

no
yes

Latitude

In Latitude, an object's truthiness is determined by its toBool method, which must return one of the constants True or False. Obviously, these two constants have trivial toBool methods which return themselves. Nil is also falsy, while most other built-in objects (including numbers, strings, arrays, etc.), including "empty" objects such as the empty string, are truthy.

By convention, objects which are used to represent failure are considered falsy. For instance, the standard library 'unit-test module provides the FailedTest object, which is returned when a unit test fails. This object (and its children) test falsy when used as a conditional.

LFE

> 'true
true
> 'false
false
> (or 'false 'false)
false
> (or 'false 'true)
true

Lingo

Lingo has the constants TRUE and FALSE. In numerical context they have the values 1 and 0. In boolean context any nonzero integer evaluates to TRUE.

put TRUE
-- 1
put FALSE
-- 0
if 23 then put "Hello"
-- "Hello"

Little

For conditionals, numeric variables (including poly variables with a number in them), evaluate to true or false based on their value.

Use the defined() buildin to test if a variable is defined.

For the rest of variable types the value depend if the variable is defined or not.

int a = 0;
int b = 1;
int c;
string str1 = "initialized string";
string str2; //  "uninitialized string";

if (a) {puts("first test a is false");}         // This should not print
if (b) {puts("second test b is true");}         // This should print
if (c) {puts("third test b is false");}         // This should not print
if (!defined(c)) {puts("fourth test is true");} // This should print
if (str1) {puts("fifth test str1 is true");}    // This should print
if (str2) {puts("sixth test str2 is false");}   // This should not print

LiveCode

true and the string "true" are both logical true, similarly for false and "false" being logical false.

Logo

Logo has predefined symbols for true and false ("true and "false), which are the values returned by predicates and required by logical operators and conditionals.

print 1 < 0    ; false
print 1 > 0    ; true
if "true [print "yes]    ; yes
if not "false [print "no]  ; no

Unlike other lispy languages, there are no other implicit conversions. You must test explicitly for zero or empty collections.

if equal? 0 ln 1 [print "zero]
if empty? [] [print "empty]    ; empty list
if empty? "|| [print "empty]   ; empty word

Lua

All values in Lua other than false or nil are considered true:

if 0 then print "0" end             -- This prints
if "" then print"empty string" end  -- This prints
if {} then print"empty table" end   -- This prints
if nil then print"this won't print" end
if true then print"true" end
if false then print"false" end      -- This does not print

M2000 Interpreter

True is -1 and False is 0 (double type), but any comparison return boolean. We can define boolean type variables.

Using Switches "+sbl" in console or Set Switches "+sbl" in code in a module, we get Prints of boolean values as True/False or Αληθές/Ψευδές

use Greek to change to 1032 locale and Greek error messages and dialogs

use Latin to change to 1033 locale and English error messages and dialogs

We can use Locale 1032 to change only locale to Greek.

M2000 print in console any character from Unicode, and diacritics (one or more, without moving the cursor).

Module CheckBoolean {
      A=True
      Print Type$(A)="Double"
      B=1=1
      Print Type$(B)="Boolean"
      Print A=B  ' true
      Print A, B   ' -1   True
      Def boolean C=True, D=False
      Print C, D , 1>-3 ' True False True
      K$=Str$(C)
      Print K$="True"  ' True
      Function ShowBoolean$(&x) {
           x=false
           Try {
                        if keypress(32) then x=true : exit
                        If Keypress(13) then exit
                        loop
            }
            =str$(x, locale)
      }
      Wait 100
      Print "C (space for true, enter for false)="; : Print ShowBoolean$(&c)
      Print C
}
CheckBoolean

Print str$(True, "\t\r\u\e;\t\r\u\e;\f\a\l\s\e")="true"
Print str$(False, "\t\r\u\e;\t\r\u\e;\f\a\l\s\e")="false"
Print str$(2, "\t\r\u\e;\t\r\u\e;\f\a\l\s\e")="true"

Maple

The keywords "true" and "false" are the default boolean values. Expressions involving relational operators are evaluated logically using the evalb command. Expressions under assumptions may be evaluated logically using the is command. Types may be tested, resulting in boolean values, using the type command.

Mathematica/Wolfram Language

True and False are the default boolean values. To make any expression a boolean use the Boole[] function.

MATLAB

The keywords "true" and "false" are the default boolean values. But, many functions prefer to return boolean "1" or "0" instead of "true" or "false". It is very important to note that having a function return a numerical 1 or 0 is not the same as a boolean "1" or "0". To make a number or array of numbers a boolean use the logical() function. logical() will convert any non-zero number to a boolean "1" and any zero entries a boolean "0".

Sample Usage: (islogical() is a function that returns a boolean "1" if the input is a boolean, "0" otherwise)

>> islogical(true)

ans =

     1

>> islogical(false)

ans =

     1

>> islogical(logical(1))

ans =

     1

>> islogical(logical(0))

ans =

     1

>> islogical(1)

ans =

     0

>> islogical(0)

ans =

     0

Maxima

is(1 < 2);
/* true */

is(2 < 1);
/* false */

not true;
/* false */

not false;
/* true */

Metafont

Metafont has the type boolean; a boolean variable can be true or false. Using non boolean values (or expressions that do not evaluate to a boolean value) results in a recoverable error; by default, any non-boolean value is interpreted as false.

min

Works with: min version 0.19.3

true and false are the only boolean values in min. The bool function converts various objects to boolean values:

• non-zero number: true
• zero number: false
• non-empty quotation: true
• empty quotation: false
• non-empty string: true
• empty string: false
• boolean: no conversion performed

MiniScript

In MiniScript, numbers represent boolean values, with additional fuzzy logic for degrees of truth. Built-in constants `true` and `false` are simply aliases for 1 and 0, respectively.

boolTrue = true
boolFalse = false

if boolTrue then print "boolTrue is true, and its value is: " + boolTrue

if not boolFalse then print "boolFalse is not true, and its value is: " + boolFalse

mostlyTrue = 0.8
kindaTrue = 0.4
print "mostlyTrue AND kindaTrue: " + (mostlyTrue and kindaTrue)
print "mostlyTrue OR kindaTrue: " + (mostlyTrue or kindaTrue)

Output:

boolTrue is true, and its value is: 1
boolFalse is not true, and its value is: 0
mostlyTrue AND kindaTrue: 0.32
mostlyTrue OR kindaTrue: 0.88

Mirah

import java.util.ArrayList
import java.util.HashMap

# booleans 
puts 'true is true' if true
puts 'false is false' if (!false)

# lists treated as booleans
x = ArrayList.new
puts "empty array is true" if x
x.add("an element")
puts "full array is true" if x
puts "isEmpty() is false" if !x.isEmpty()

# maps treated as booleans
map = HashMap.new
puts "empty map is true" if map
map.put('a', '1')
puts "full map is true" if map
puts "size() is 0 is false" if !(map.size() == 0)

# these things do not compile
# value = nil   # ==> cannot assign nil to Boolean value
# puts 'nil is false' if false == nil  # ==> cannot compare boolean to nil
# puts '0 is false' if (0 == false)    # ==> cannot compare int to false

#puts 'TRUE is true' if TRUE   # ==> TRUE does not exist
#puts 'FALSE is false' if !FALSE   # ==> FALSE does not exist

Modula-2

MODULE boo;

IMPORT  InOut;

VAR     result, done            : BOOLEAN;
        A, B                    : INTEGER;

BEGIN
   result := (1 = 2);
   result := NOT result;
   done := FALSE;
   REPEAT
     InOut.ReadInt (A);
     InOut.ReadInt (B);
     done := A > B
   UNTIL done
END boo.

Modula-3

Similar to Ada, Modula-3 has a built-in BOOLEAN type defined as

TYPE BOOLEAN = {FALSE, TRUE}

Monte

Much like E, Monte has built-in objects true and false, and a boolean guard.

def example(input :boolean):
    if input:
        return "Input was true!"
    return "Input was false."

MUMPS

M[UMPS] has no data types per se, however, any value can be coerced to a specific interpretation by applying certain operators.

Internally, the language treats any "zero" value as a "false", and any "non-zero" value as a "true".
Values like 1, 2, 13245.08763, .1, "0.00001234ABC" and "1234ABC" are "true".
Values like 0, -3, "", " 123" (note the leading space in this one), "+++++567", "abc", "abc1245" are "false".

When a boolean operator is applied to an operand, the value of that operand is coerced to a logical value, that is: if the value starts out with a sequence of digits that look like a non-zero number, the value is "true" (1), and otherwise that value is "false" (0).

There are two standardized binary boolean operators: & (and) and ! (or). Newer implementations of the language may also support !! (exclusve or). There is one unary boolean operator: ' (not).

Nanoquery

a = true
b = false

if a
    println "a is true"
else if b
    println "b is true"
end

Output:

a is true

Neko

Neko includes a bool boolean data type, true and false. Conditional execution flow only reacts to bool, numeric values test as false as are string literals.

Neko also includes two low level builtins: $not(value) and $istrue(value). These return bool results. $not returning true if value is false, 0 or null. $istrue returning true if value is not false, not 0 and not null.

/* boolean values */
$print(true, "\n");
$print(false, "\n");

if 0 {
  $print("literal 0 tests true\n");
} else {
  $print("literal 0 tests false\n");
}

if 1 {
  $print("literal 1 tests true\n");
} else {
  $print("literal 1 tests false\n");
}

if $istrue(0) {
  $print("$istrue(0) tests true\n");
} else {
  $print("$istrue(0) tests false\n");
}

if $istrue(1) {
  $print("$istrue(1) tests true\n");
} else {
  $print("$istrue(1) tests false\n");
}

Output:

prompt$ nekoc boolean.neko
prompt$ neko boolean
true
false
literal 0 tests false
literal 1 tests false
$istrue(0) tests false
$istrue(1) tests true

Nemerle

In Nemerle, boolean values are held in variables of type bool, and can be either true or false. Comparison expressions evaluate to boolean values as well.

NetRexx

NetRexx inherits boolean functionality directly from the Java virtual machine with the exception that the true and false keywords are not defined to the language. Defining true and false variables can lead to name collisions during compilation so a simple expedient is to define boolean functions isTrue and isFalse to return the appropriate values.

/* NetRexx */
options replace format comments java crossref savelog symbols nobinary

bval = [1, 0, 5, 'a', 1 == 1, 1 \= 1, isTrue, isFalse]

loop b_ = 0 for bval.length
  select case bval[b_]
    when isTrue  then say bval[b_] 'is true'
    when isFalse then say bval[b_] 'is false'
    otherwise         say bval[b_] 'is not boolean'
    end
  end b_

method isTrue public static returns boolean
  return (1 == 1)

method isFalse public static returns boolean
  return \isTrue

Output:

1 is true
0 is false
5 is not boolean
a is not boolean
1 is true
0 is false
1 is true
0 is false

Nim

if true: echo "yes"
if false: echo "no"

# Other objects never represent true or false:
if 2: echo "compile error"

Oberon-2

VAR
  a,b,c: BOOLEAN;
...
  a := TRUE;
  b := FALSE;
  c := 1 > 2;

Objeck

Objeck has a Bool type that is set to either true or false. By default boolean types are initialized to false. The boolean type also allows methods to be invoked, which perform simple conversions or print given values.

Object Pascal

In addition to the Boolean type defined by standard Pascal, object Pascal defines the types byteBool, wordBool and longBool, having a sizeOf one, two, or four bytes respectively. They were introduced primarily to ease interfacing with code written in other languages, such as C. These types only have ord(false) defined as zero, and any other ordinal value represents true.

Nonetheless, Boolean is the preferred type.

See also Delphi and Free Pascal

Objective-C

Objective-C follows pretty much the same rules as C. In addition to C, Objective-C has a BOOL boolean type, with values YES for true and NO for false. Objective-C also adds several special types of pointers; for pointers to objects (values of type id), the nil pointer is false, everything else is true; for pointers to classes (values of type Class), the Nil pointer is false, everything else is true.

OCaml

OCaml defines a built-in data type bool, which has exactly two members, represented by the keywords true and false:

type bool = false | true

In addition to all the functionality of any other OCaml algebraic data type (e.g. pattern matching), and the functionality of any other OCaml data type (e.g. comparisons false = false, false < true, etc.), bool is also used in the guards in pattern matching (“when”) and if and while syntaxes.

As with any other OCaml data type, there are no automatic conversions of other types to bool.

Octave

Octave uses true (1) and false (0). The class of a variable holding a boolean value is logical, which however can be casted to a numeric class, so that r = true; r * 2 gives 2 as result. Any non-zero value is interpreted as true, and 0 as false.

Oforth

Oforth uses true (1) and false (0)

Any non-zero value is interpreted as true, and 0 as false.

Ol

#true is True, #false is False; #t is synonym for #true, #f is synonym for #false.

In conditionals everything that is not #false is True.

p.s. Empty lists - '() - in conditionals is True.

ooRexx

.true or 1 are true, .false or 0 are false

Order

Order supplies the keywords 8true and 8false. Other types are not supposed to automatically convert to any boolean value (in practice some may do so due to implementation quirks, but this is not reliable).

Oz

true and false are the only boolean values. No other values are automatically converted to bool.

PARI/GP

Generally, false is 0 and true is nonzero. Certain other values also behave as false, like the vector [0]. Built-in boolean functions use 0 and 1 (but note that some functions like ispower are not boolean!).

The details of what is considered true or false is contained in see the function gequal0:

• An integer (t_INT), polynomial (t_POL), power series (t_SER), or element of a finite field (t_FFELT) is false if and only if it is 0.
• A real number (t_REAL) or complex number (t_COMPLEX) is false if and only if its absolute value rounds to 0 at the object's precision. Note that this can make nonzero complex numbers (with tiny norm) false.
• An integer mod m (t_INTMOD) is false if and only if its residue class is 0, i.e., if lift(x) is 0.
• A p-adic number (t_PADIC) is false if and only if it is zero up to the object's p-adic precision is 0, i.e., if lift(x) is 0.
• A vector (t_VEC), column vector (t_COL), or matrix (t_MAT) is false if and only if all of its components are 0. Note that [] is thus false.
• t_QUAD, t_POLMOD, t_RFRAC

Pascal

Pascal defines the type Boolean as a “special” enumeration type with exactly two elements: false and true. It is guaranteed that ord(false) is 0 and ord(true) is 1.

There is no automatic conversion from integer values to Boolean values, as it is prevalent in many other languages. Instead, one has to write a Boolean expression, for example myInteger <> 0 in order to get an assignment-compatible type.

See also Delphi, Free Pascal, and Object Pascal

Perl

my $x = 0.0;
my $true_or_false = $x ? 'true' : 'false';     # false

or

my $x = 1;          # true

my $true_or_false;

if ($x) {
    $true_or_false = 'true';
}
else {
    $true_or_false = 'false';
}

The values in Perl that are false are: 0 (as a number (including 0.0), or as the string '0', but not the string '0.0'), the empty string '', the empty list (), and undef. Everything else is true. See perlsyn.

Short circuit evaluations

Boolean comparison of zero against itself gives a value of one, but Perl uses short circuit evaluations, so any true or false value may be returned from a boolean expression:

print (7 && 2);  # 2, rather than 1(true)
print (2 && 7);  # 7, rather than 1(true)
print (7 xor 2); # empty string, rather than 0(false)
print ('apples' && 'pears');  # pears, rather than 1(true)
print ('apples' xor 'pears'); # empty string, rather than 0(false)

Objects

Objects may break these rules at will via overloading.

There are no keywords for true and false

Perl has no builtin "true" or "false" keywords. An old trick of using them as bareword strings is strongly discouraged in modern Perl.

Special cases

As a special case, literal 1s and 0s will never cause a "Useless use of a constant in void context" warning. Another special case worth pointing out here is that the string '0 but true' won't provoke a warning if it's used as a number.

Phix

Zero is false, any other number is true. Attempting to use a string or sequence as a boolean is assumed to be a programming logic blunder and causes a fatal run-time error.

Conditions such as if length(s) then are permitted, but the more explicit if length(s)!=0 then is generally preferred, and conversely, if flag then is to be preferred over if flag=true then. Comparison operators evaluate to 1(true) or 0(false). A boolean test is inverted by preceding it with the keyword not. The null character ('\0') is considered false, all other characters are deemed true. The builtin constants TRUE/FALSE and their aliases True/true/False/false may also be used.

There is however a gotcha in JavaScript, and hence pwa/p2js, in that true !== 1 and false !== 0. In almost all other respects, true is 1 and false is 0, for instance 1+true evaluates to 2, just like desktop/Phix. It is only direct comparison for equality of booleans and numbers using an infix operator which fails, and I suppose you could argue that is a programming logic blunder, by which I mean in a particular source file of a specific application, rather than in the (Phix or JavaScript) programming language definition. There is no such issue with equal() and compare(), which pwa/p2js automatically maps to when needed, that is except for bool vs number, which is difficult because in desktop/Phix those are the same thing. Thankfully, there are very few places anyone ever actually compares bools against 0 and 1 using an infix operator.

The following example illustrates, and also emphasies the subtlety of the issue (no difference whatsoever if c, d, e, f are defined as bool):

with javascript_semantics
for i=1 to 3 do
    integer c = (i==2),         -- fine
            d = (c==1),         -- oops
            e = (c==true),      -- fine
            f = equal(c,1)      -- fine, ditto equal(c,true)
    printf(1,"%d==2:%5t(%d) ==1:%5t, eq1:%5t, ==true:%5t\n",
              {i,     c, c,       d,       e,          f})
end for
--
-- output on desktop/Phix: 1==2:false(0) ==1:false, eq1:false, ==true:false
--                         2==2: true(1) ==1: true, eq1: true, ==true: true
--                         3==2:false(0) ==1:false, eq1:false, ==true:false
--
-- output on pwa/p2js:     1==2:false(0) ==1:false, eq1:false, ==true:false
--                         2==2: true(1) ==1:false, eq1: true, ==true: true
--                         3==2:false(0) ==1:false, eq1:false, ==true:false
--

PHP

The values in PHP that are false are: FALSE, NULL, the number 0 (as an integer 0, float 0.0, or string '0', but not the string "0.0"), the empty string "", the empty array array(), and "SimpleXML objects created from empty tags"(?).

Everything else is true. The keyword TRUE exists. [1]

Picat

Picat has the built-in true/0 for true (it always succeeds) and false/0 (or fail/0) for false. false/0 (/fail/0) can be used to generate other solutions through backtracking.

go ?=>
  member(N,1..5),
  println(N),
  fail, % or false/0 to get other solutions
  nl.
go => true.

Output:

1
2
3
4
5

In the Picat shell, truth is represented as "yes" and false as "no".

Picat> 2==2

yes

Picat> 2==3

no

PicoLisp

Like in all Lisps, the symbol 'NIL' denotes "false", any other value "true". PicoLisp also uses NIL as the empty list, so the empty list is false.

Some functions return the symbol 'T' for "true" if no other useful (non-NIL) value is available in the given context. Note that 'NIL' and 'T' are written in uppercase letters (PicoLisp is case-sensitive).

Pike

> 0;
(3) Result: 0
> false;
(4) Result: 0
> 0;
(6) Result: 0
> !true;
(7) Result: 0
> true;
(8) Result: 1
> 1;
(9) Result: 1
>

PL/I

True is '1'b and false is '0'b.

Declare x bit(1);
x='1'b; /* True */
x='0'b; /* False */

Using the macro facility one can define reasonable symbols for true and false

*process source attributes xref macro or(!);
 tf: proc options(main);
 %Dcl true char; %true='''1''b';
 %Dcl false char; %false='''0''b';
 If true Then
   Put Skip list('That''s true');
 If false Then
   Put Skip List('ERROR');
 Else
   Put Skip List('false was recognized');
 End;

Output:

That's true
false was recognized

PL/M

In PL/M, even numbers are falsy and odd numbers are truthy. That is to say, conditional expressions test only the low bit of the value.

IF 0 THEN /* THIS WON'T RUN */;
IF 1 THEN /* THIS WILL */;
IF 2 THEN /* THIS WON'T */;
IF 3 THEN /* THIS WILL */;

Canonically, false is represented by 0 (all bits clear), and true by 0FFH (all bits set). These are the values that conditional operators (like =) return.

DECLARE A BYTE;
A = 4 < 5;
/* A IS NOW 0FFH */

Boolean literals are not included by default, but it is not uncommon for programmers to define them by hand:

DECLARE FALSE LITERALLY '0', TRUE LITERALLY '0FFH';

Plain English

Boolean values are called flags. The flag literals are yes and no. You can set and clear flags.

Pony

Boolean values are true and false. Conditions must have type Bool, i.e. they are always true or false.

PostScript

Predefined constants are:

true
false

PowerShell

Two automatic variables exist for this purpose:

$true
$false

However, nearly everything can be converted to a boolean value, as detailed in the following list:

• any non-zero number evaluates to true, zero evaluates to false
• any non-empty string evaluates to true, an empty string evaluates to false
• an empty array evaluates to false
• an array containing exactly one item evaluates to whatever the only item evaluates to
• any array with more than one item evaluates to true
• a reference to any object evaluates to true, $null evaluates to false

Python

Python has a boolean data type with the only two possible values denoted by True and False.

The boolean type is a member of the numeric family of types (specifically a subclass of int), and when used in a numeric, but not boolean context, True has the value one and False the value zero. Also hash(True) == hash(1) and same goes for False and 0. Conversely, when numbers are used in a boolean context, zero is false and anything other than zero is true. (Note however, that True is equal to 1, so for example True + True != True.)

In a boolean context, Python extends what is meant by true and false by accepting empty collection types, such as an empty dict or an empty list as being False, and non-empty collection types as being True, so in an if statement one might branch on a list which would be the same as testing if the list had any contents.

In Python 2, a user-created class that defines a __nonzero__ method to return False or 0, or whose __len__ method returns 0, will be treated as False, otherwise the instance is treated as True. In Python 3, the magic method __nonzero__ has been changed to __bool__, which can only return values of type bool (not even int or None).

None is also False in a boolean context.

Some examples:

>>> True
True
>>> not True
False
>>> # As numbers
>>> False + 0
0
>>> True + 0
1
>>> False + 0j
0j
>>> True * 3.141
3.141
>>> # Numbers as booleans
>>> not 0
True
>>> not not 0
False
>>> not 1234
False
>>> bool(0.0)
False
>>> bool(0j)
False
>>> bool(1+2j)
True
>>> # Collections as booleans
>>> bool([])
False
>>> bool([None])
True
>>> 'I contain something' if (None,) else 'I am empty'
'I contain something'
>>> bool({})
False
>>> bool("")
False
>>> bool("False")
True

Quackery

Translation of: Forth

In conditionals, zero is false, non-zero is true. There are predefined words for the canonical forms, false returns zero and true returns 1.

R

Similarly to Octave, R uses TRUE and FALSE, kept in variable of class logical, which is silently casted to 1 (TRUE) or 0 (FALSE) if used as numeric value. The opposite is also true: the value 0 can be used as FALSE, and non-zero numbers as TRUE.

The values T and F are given the values TRUE and FALSE respectively (for compatibility with S-Plus), though these may be changed to other values by the user.

Racket

Racket has the standard Scheme Boolean values #t and #f, and will also accept #true and #false. This is a literal syntax, so it can be used anywhere including in quoted positions. There are also bindings for true and false (but of course when these are quoted, the result is plain symbols). Like other Scheme descendants, many conditional constructs treat any non-false value as "truthy." So, for instance,

(cond ([(< 4 3) 'apple]
       ['bloggle 'pear]
       [else 'nectarine])

... evaluates to 'pear, because 'bloggle is not false.

Raku

(formerly Perl 6)

Works with: Rakudo version 2015.12

Raku provides an enumeration Bool with two values, True and False. Values of enumerations can be used as ordinary values or as mixins:

my Bool $crashed = False;
my $val = 0 but True;

For a discussion of Boolean context (how Raku decides whether something is True or False): https://docs.raku.org/language/contexts#index-entry-Boolean_context.

Raven

Raven considers 0 as FALSE, -1 as TRUE

TRUE print
FALSE print
2 1 > print   # TRUE (-1)
3 2 < print   # FALSE (0)
42 FALSE !=   # TRUE (-1)

REBOL

REBOL uses values of type logic! to represent boolean values. A boolean value can be 'true' or 'false', which also happen to be understood as predefined constants. Other constants are also provided to improve program readability:

logic! Constants

True	False
true	false
yes	no
on	off
any [block! series! date! number! string! ...]	none

As the last true value implies, pretty much any other type will evaluate to true. This is important to remember if you're used to a language where the value "0" is considered to be false -- in REBOL, it's true.

ReScript

A ReScript boolean has the type bool and can be either true or false.

ReScript's true/false compiles into a JavaScript true/false.

Retro

Zero is false and non-zero is true. Comparison functions return -1 for true and 0 for false.

REXX

The REXX language enforces the values for   true   and   false,   only the two values are valid:

• 0     (zero)   [for false]
• 1     (one)     [for true]

The following aren't   true   or   false:

• 0.
• 0.0
• 00
• 1.
• 1.0
• 001
• +1
• 2
•       (a null value, that is, length=0)
• any value with a blank before/in/after the value.

simplistic

 true = 1
false = 0

spruced up

Some programmers like to "spruce up" such a simple assignment:

true  = (1=1)
false = (1=0)

more exactitudeness

true  = (1==1)
false = (1==0)

oblique

true  = (1==1)
false = \true

[The parentheses aren't necessary in all of the above versions.]

Some REXX interpreters allow the   NOT   (¬) character for negation:

false = ¬true

esoteric

true  =            1984  =  1984
false =           'war'  =  'peace'
false =       'freedom'  =  'slavery'
false =     'ignorance'  =  'strength'

Of course, in Orwellian terms, the above   false   statements are   true,   but REXX isn't an Eric Arthur Blair reader.

Ring

x = True
y = False
see "x and y : " + (x and y) + nl
see "x or y : " + (x or y) + nl
see "not x : " + (not x) + nl

Rockstar

There are several synonyms for true and false. These include yes and no, or right and wrong. Therefore, to make a variable called Alice true and a variable called Bob false, you can write this.

Alice was right.
Bob was wrong.

RPL

There is no boolean variable type in RPL. Boolean values are real numbers, zero meaning 'FALSE' and any other value meaning 'TRUE'; built-in boolean operators and functions always return 1 for TRUE. RPL users have also access to boolean registers named flags, identified by a number, that can be cleared, set or tested.

Works with: Halcyon Calc version 4.2.7

1 == 1  
1 == 2
≪ IF 42 THEN "TRUE" ELSE "FALSE" END ≫ EVAL
14 CF 14 FS?
14 SF 14 FS?

Output:

5: 1
4: 0
3: "TRUE"
2: 0
1: 1

Ruby

The only values in Ruby that are false are: false and nil. They have synonyms FALSE and NIL.

Everything else is true. Constants true (and TRUE) exist. Note for Python and Perl users: unlike Python, in Ruby, the number 0, the empty string, the empty array, and the empty hash, etc. are all true; you can instead use the zero? method to test for 0, and the .empty? method to test for an empty sequence.

false, nil and true are singleton instances of classes FalseClass, NilClass and TrueClass respectively. [2]

Rust

fn main() {
    // Rust contains a single boolean type: `bool`, represented by the keywords `true` and `false`.
    // Expressions inside `if` and `while` statements must result in type `bool`. There is no
    // automatic conversion to the boolean type.

    let true_value = true;
    if true_value {
        println!("foo is {}.", true_value);
    }

    let false_value = false;
    if !false_value {
        println!("bar is {}.", false_value);
    }
}

Output:

foo is true.
bar is false.

Sather

The BOOL type can be true or false. Sather never implicitly does casting of a type in another, so numeric value or other types cannot be used (implicitly) as boolean value; nonetheless an explicit "cast" can be done:

v:BOOL := true; -- ok
i:INT := 1;
v := 1; -- wrong 
if i then ... end; -- wrong: if requires a bool!
-- BUT
v := 1.bool; -- ok
if i.bool then ... end; -- ok

In this case, 0.bool is false, and n.bool with n not equal to 0 is true.

S-BASIC

Although S-BASIC has no explicit boolean data type, it allows integer, real, fixed, string, and character variables to hold the results of boolean operations and to represent true and false conditions in IF, WHILE, and REPEAT statements. For types real.double, real, and fixed, a value of zero is false, and any non-zero value is true. For integers, the value 0 is treated as false, while -1 (or FFFFH), the bit-wise negation of zero, is treated as true. For characters and strings, 'Y', 'y', 'T', and 't' are treated as true, while 'N', 'n', 'F', and 'f' are treated as false. (For strings, only the first character is considered.) For convenience, the $CONSTANT compiler directive can be used to provide values for "true" and "false".

$constant true = 0FFFFH
$constant false = 0

var a, another = char
var b, adult, age = integer
var c = real

repeat
   begin
     input "Applicant's age in years"; age
     adult = (age >= 18)
     if adult then
        print "Applicant has full access"
     else
        print "Applicant has restricted access"
     input "Do another (y/n)"; another
   end
until not another

a = (2 > 3)
b = (2 > 3)
c = (2 > 3)
print "2 > 3 as char: "; a
print "2 > 3 as int : "; b
print "not (2 > 3)  : "; not b
print "2 > 3 as real: "; c
print "not (2 > 3)  : "; not c
 
end

Output:

Applicant's age in years? 19
Applicant has full access
Do another (y/n)? n
2 > 3 as char: F
2 > 3 as int : 0
not (2 > 3)  :-1
2 > 3 as real: 0
not (2 > 3)  :-1

Scala

Booleans in Scala are given by the literals true and false, case sensitive, which are the only instances of the class Boolean.

Scheme

The only value in Scheme that is false is #f.

Everything else (including the empty list, unlike Lisp) is true. The constant #t represents the canonical true value.

Seed7

Seed7 defines the type boolean. The only values of boolean are TRUE and FALSE. There are no automatic conversions from any other types into boolean, and it is a compile-time error to use any type other than boolean in a place that expects a boolean (e.g. if-statement condition, while-statement condition, operand of a logical operator, etc.).

Self

Self has two objects, true and false.

SenseTalk

True, Yes, and On are true; False, No, Off and Empty (an empty string) are false.

repeat with each item of [True, False, Yes, No, On, Off, ""]
	put it & " is " & (it is true)
end repeat

Output:

True is True
False is False
Yes is True
No is False
On is True
Off is False
 is False

Sidef

Sidef defines the true and false boolean values, which are part of the Bool type.

var t = true;
var f = false;

In conditional expressions, anything that evaluates to zero or nothing is considered false, including empty arrays and empty hashes.

if (0 || "0" || false || nil || "" || [] || :()) {
    say "true"
} else {
    say "false";
}

Output:

false

Simula

Simula has true and false keywords, representing the only values of type boolean. There are no automatic conversions from any other types into boolean, and it is a compile-time error to use any type other than boolean in a place that expects a boolean (e.g. if-statement condition, while-statement condition, operand of a logical operator, etc.).

Slate

Use True or False.

Smalltalk

Use "true" and "false".
Smalltalk uses the Boolean class, which has two subclasses (True and False). true and false are singleton instances of those classes. E.g. an expression like 5 = 5 returns true.

SNUSP

Zero is false and non-zero is true, as used by the sole skip-if-zero operator (?).

$!/?\=false= + =true=#
  \-/

SPL

In SPL zero is false, any other value is true.

Standard ML

Standard ML defines a top-level data type bool, which has exactly two members, true and false:

datatype bool = false | true

In addition to all the functionality of any other Standard ML algebraic data type (e.g. pattern matching, equality false = false), bool is also used in if and while syntaxes.

As with any other Standard ML data type, there are no automatic conversions of other types to bool.

Stata

Stata uses the values 0 for "false" and 1 for "true". In expressions involving boolean operators, any nonzero numeric value (including missing values) is considered true.

Swift

Swift defines a built-in data type Bool, which has two values, represented by the keywords true and false. There is no conversion between booleans and other data types. Conditionals require a type that conforms to the BooleanType protocol, which provides a conversion to Bool for that type; types that conform include Bool and some other types.

Tcl

True values

1 (or other non-zero number, e.g., 42), true, yes, on

False values

0 (or other zero number, e.g., 0.0), false, no, off

Any of these values may be abbreviated, and mixed-case spellings are also acceptable. [3] Any other value gives an error. In an interactive tclsh session:

% if {""} then {puts true} else {puts false}
expected boolean value but got ""

Test for the boolean value of a string can be stuff like

if {[string is false -strict $string]} ...

which will test for "no" or "NO" or "0" or "False" or ...

Trith

The boolean constants are true and false. In a conditional context, the only false values are false and nil -- every other value is true.

UNIX Shell

The traditional Bourne shell does not provide a reserved keyword for true or false.

Truth is determined by exit codes rather than values

The evaluation of true and false within the shell is different to the evaluation of truth from within a high level language. Within the shell, a truth is based on the exitcode of the last command in the evaluation block:

• An exitcode of zero is considered to be a true condition
• An exitcode of nonzero is considered to be a false condition

In the following example, after running the test command, the then syntactical component runs the optional branch if an exitcode is of zero determined:

if
  echo 'Looking for file'  # This is the evaluation block
  test -e foobar.fil       # The exit code from this statement determines whether the branch runs                            
then
  echo 'The file exists'   # This is the optional branch
  echo 'I am going to delete it' 
  rm foobar.fil
fi

In some later shells, the values true and false are defined, respectively, as a return code of 0 and a return code of greater-than zero. While there are built-in functions for each of these values, booleans are most commonly the result of a test or a process termination.

Works with: bash

Works with: ksh

true && echo "true" || echo "false"

Ursa

Ursa has the boolean data type which can be declared using the declare (or decl) function.

decl boolean bool

Boolean values can be set to either true or false, or the result of an expression.

set bool true
# same as
set bool (= 2 2)

or

set bool false
# same as
set bool (not (= 2 2))

VBA

VBA has a boolean type. As an integer False is 0 and anything else is True. However True converts to -1. Booleans are False by default.

Dim a As Integer
Dim b As Boolean
Debug.Print b
a = b
Debug.Print a
b = True
Debug.Print b
a = b
Debug.Print a

Output:

Output of above lines:

False
0
True
-1

VBScript

VBScript has the boolean subdatatype and also the two constants True and False. When converting an integer to a boolean, 0 is False and anything not equal to 0 is True.

a = True
b = False
Randomize Timer
x = Int(Rnd * 2) <> 0
y = Int(Rnd * 2) = 0
MsgBox a & " " & b & " " & x & " " & y

Output:

True False True False

Vim Script

A non-zero Number is true, 0 is false.

Since a String is converted automatically to a Number when necessary, the following will print "false" because "foo" is converted to 0:

if "foo" 
    echo "true"
else
    echo "false"
endif

V (Vlang)

V has a bool type, with literal values for true and false. Numeric values are not used in conditional statements. 0 is not treated as false, and non-zero does not mean true, in V.

// Boolean Value, in V
// Tectonics: v run boolean-value.v
module main

// V bool type, with values true or false are the V booleans.
// true and false are V keywords, and display as true/false
// Numeric values are not booleans in V, 0 is not boolean false
pub fn main() {
    t := true
    f := false

    if t { println(t) }

    // this code would fail to compile
    // if 1 { println(t) }

    if 0 == 1 { println("bad result") } else { println(f) }
}

Output:

prompt$ v run boolean-value.v
true
false

WDTE

WDTE has a built-in boolean type, the two values of which are exposed by the std package's true and false functions. In general, however, built-in conditional functionality, such as switch expressions, considers any value that is not true to be false.

let io => import 'io';
let ex => switch 'this is irrelevant for this example' {
  false => 'This is, obviously, not returned.';
  'a string' => 'This is also not returned.';
  true => 'This is returned.';
};
ex -- io.writeln io.stdout;

The above prints "This is returned."

Wren

Wren has a core class, Bool, which has two instances true and false which are also reserved words in the language.

This class has two methods: the operator ! which returns the logical complement of its receiver and toString which returns its string representation.

var embed = true
System.printAll([embed, ", ", !embed, ", ", "Is Wren embeddable? " + embed.toString])

Output:

true, false, Is Wren embeddable? true

XLISP

Boolean "false" may be represented by #F, #!FALSE, NIL, or the empty list; any other value is counted as true in conditional expressions, but it is also possible to represent the Boolean value "true" using your choice of the symbols #T, #!TRUE, and T. All these symbols are case-insensitive. Note that T, unlike the others, is a variable: it is bound by default to the constant #T, but you can (although you shouldn't) assign it any other value including "false" (by doing something like (setq t nil)). Boolean values are printed as #T and ().

XPL0

An integer value equal to 0 is false, and a value not equal to 0 is true. Relational operations evaluate to 0 for false and -1 for true. The command word 'true' equals -1, and 'false' equals 0.

XSLT

<xsl:if test="true() or false()">
  True and false are returned by built-in XPath functions.
</xsl:if>
<xsl:if test="@myAttribute='true'">
  Node attributes set to "true" or "false" are just strings. Use string comparison to convert them to booleans.
</xsl:if>
<xsl:if test="@myAttribute or not($nodeSet)">
  Test an attribute for its presence (empty or not), or whether a node set is empty.
</xsl:if>

Z80 Assembly

There are no official constants for True or False, however the common convention is to use 0 for false and nonzero for true. In reality, any mutually exclusive condition will work. True/False can be tested using a variety of instructions. The most common are CP and BIT but in certain cases it can be done faster using AND or even RRCA.

All of the following can be used to test if the rightmost bit of a byte is 1.

BIT 0,A
jr nz,true
;;;;;;;;;;;;;;;;
AND 1
jr nz,true
;;;;;;;;;;;;;;;;
RRCA
jr c,true

Of these three methods, the last one is the fastest and takes the least amount of bytes to encode. However, it does destroy the variable, which may not be an option depending on what you need to do with that data later. BIT is slower than the rest but doesn't alter registers or memory, just the flags, which is sometimes exactly what you need.

zkl

a:=True;
b:=False;
True.dir();

Output:

True : Bool
Methods:
   -- BaseClass Method Property __sGet __sSet copy create dir fp fp1 fp2 
   fpM fpN isChildOf isInstanceOf isType len method noop print println 
   property resolve toBool toData toFloat toInt toList toString toType 
Properties:
   -- createReturnsSelf fullName id isContainer isThreadSafe itype methods 
   name numObjects oID otype properties size type typeID vaultPath

zonnon

var
	a,b,c: boolean;
begin
	a := false;
	b := true;
	c := 1 > 2;
...