Short-circuit evaluation: Difference between revisions

Content added Content deleted

Inline

Revision as of 13:10, 27 April 2021

Assume functions a and b return boolean values, and further, the execution of function b takes considerable resources without side effects, and is to be minimized.

If we needed to compute the conjunction (and):

x = a() and b()

Then it would be best to not compute the value of b() if the value of a() is computed as false, as the value of x can then only ever be false.

Similarly, if we needed to compute the disjunction (or):

y = a() or b()

Then it would be best to not compute the value of b() if the value of a() is computed as true, as the value of y can then only ever be true.

Some languages will stop further computation of boolean equations as soon as the result is known, so-called short-circuit evaluation of boolean expressions

Task

Create two functions named a and b, that take and return the same boolean value.

The functions should also print their name whenever they are called.

Calculate and assign the values of the following equations to a variable in such a way that function b is only called when necessary:

x = a(i) and b(j)

y = a(i) or b(j)

If the language does not have short-circuit evaluation, this might be achieved with nested if statements.

11l

Translation of: Python

<lang 11l>F a(v)

  print(‘  ## Called function a(#.)’.format(v))
  R v

F b(v)

  print(‘  ## Called function b(#.)’.format(v))
  R v

L(i) (0B, 1B)

  L(j) (0B, 1B)
     print("\nCalculating: x = a(i) and b(j)")
     V x = a(i) & b(j)
     print(‘Calculating: y = a(i) or  b(j)’)
     V y = a(i) | b(j)</lang>

Output:


Calculating: x = a(i) and b(j)
  # Called function a(0B)
Calculating: y = a(i) or  b(j)
  # Called function a(0B)
  # Called function b(0B)

Calculating: x = a(i) and b(j)
  # Called function a(0B)
Calculating: y = a(i) or  b(j)
  # Called function a(0B)
  # Called function b(1B)

Calculating: x = a(i) and b(j)
  # Called function a(1B)
  # Called function b(0B)
Calculating: y = a(i) or  b(j)
  # Called function a(1B)

Calculating: x = a(i) and b(j)
  # Called function a(1B)
  # Called function b(1B)
Calculating: y = a(i) or  b(j)
  # Called function a(1B)

Ada

Ada has built-in short-circuit operations and then and or else: <lang Ada>with Ada.Text_IO; use Ada.Text_IO;

procedure Test_Short_Circuit is

  function A (Value : Boolean) return Boolean is
  begin
     Put (" A=" & Boolean'Image (Value));
     return Value;
  end A;
  function B (Value : Boolean) return Boolean is
  begin
     Put (" B=" & Boolean'Image (Value));
     return Value;
  end B;

begin

  for I in Boolean'Range loop
     for J in Boolean'Range loop
        Put (" (A and then B)=" & Boolean'Image (A (I) and then B (J)));
        New_Line;
     end loop;
  end loop;
  for I in Boolean'Range loop
     for J in Boolean'Range loop
        Put (" (A or else B)=" & Boolean'Image (A (I) or else B (J)));
        New_Line;
     end loop;
  end loop;

end Test_Short_Circuit;</lang>

Sample output:

 A=FALSE (A and then B)=FALSE
 A=FALSE (A and then B)=FALSE
 A=TRUE B=FALSE (A and then B)=FALSE
 A=TRUE B=TRUE (A and then B)=TRUE
 A=FALSE B=FALSE (A or else B)=FALSE
 A=FALSE B=TRUE (A or else B)=TRUE
 A=TRUE (A or else B)=TRUE
 A=TRUE (A or else B)=TRUE

ALGOL 68

With Standard

Works with: ALGOL 68 version Revision 1 - no extensions to language used

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

Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8-8d

Note: The "brief" conditional clause ( ~ | ~ | ~ ) is a the standard's shorthand for enforcing short-circuit evaluation. Moreover, the coder is able to define their own proc[edures] and op[erators] that implement short-circuit evaluation by using Algol68's proceduring. <lang algol68>PRIO ORELSE = 2, ANDTHEN = 3; # user defined operators # OP ORELSE = (BOOL a, PROC BOOL b)BOOL: ( a | a | b ),

  ANDTHEN = (BOOL a, PROC BOOL b)BOOL: ( a | b | a );

user defined Short-circuit_evaluation procedures #

PROC or else = (BOOL a, PROC BOOL b)BOOL: ( a | a | b ),

    and then = (BOOL a, PROC BOOL b)BOOL: ( a | b | a );

test:(

 PROC a = (BOOL a)BOOL: ( print(("a=",a,", ")); a),
      b = (BOOL b)BOOL: ( print(("b=",b,", ")); b);

CO

Valid for Algol 68 Rev0: using "user defined" operators #
Note: here BOOL is being automatically "procedured" to PROC BOOL #

 print(("T ORELSE F = ", a(TRUE) ORELSE b(FALSE), new line));
 print(("F ANDTHEN T = ", a(FALSE) ANDTHEN b(TRUE), new line));

 print(("or else(T, F) = ", or else(a(TRUE), b(FALSE)), new line));
 print(("and then(F, T) = ", and then(a(FALSE), b(TRUE)), new line));

END CO

Valid for Algol68 Rev1: using "user defined" operators #
Note: BOOL must be manually "procedured" to PROC BOOL #

 print(("T ORELSE F = ",  a(TRUE) ORELSE  (BOOL:b(FALSE)), new line));
 print(("T ORELSE T = ",  a(TRUE) ORELSE  (BOOL:b(TRUE)), new line));

 print(("F ANDTHEN F = ", a(FALSE) ANDTHEN (BOOL:b(FALSE)), new line));
 print(("F ANDTHEN T = ", a(FALSE) ANDTHEN (BOOL:b(TRUE)), new line));

 print(("F ORELSE F = ",  a(FALSE) ORELSE  (BOOL:b(FALSE)), new line));
 print(("F ORELSE T = ",  a(FALSE) ORELSE  (BOOL:b(TRUE)), new line));

 print(("T ANDTHEN F = ", a(TRUE) ANDTHEN (BOOL:b(FALSE)), new line));
 print(("T ANDTHEN T = ", a(TRUE) ANDTHEN (BOOL:b(TRUE)), new line))

)</lang>

Output:

a=T, T ORELSE F = T
a=T, T ORELSE T = T
a=F, F ANDTHEN F = F
a=F, F ANDTHEN T = F
a=F, b=F, F ORELSE F = F
a=F, b=T, F ORELSE T = T
a=T, b=F, T ANDTHEN F = F
a=T, b=T, T ANDTHEN T = T

With Extensions

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

Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8-8d

<lang algol68>test:(

 PROC a = (BOOL a)BOOL: ( print(("a=",a,", ")); a),
      b = (BOOL b)BOOL: ( print(("b=",b,", ")); b);

Valid for Algol 68G and 68RS using non standard operators #

 print(("T OREL F = ",  a(TRUE) OREL  b(FALSE), new line));
 print(("T OREL T = ",  a(TRUE) OREL  b(TRUE), new line));

 print(("F ANDTH F = ", a(FALSE) ANDTH b(FALSE), new line));
 print(("F ANDTH T = ", a(FALSE) ANDTH b(TRUE), new line));

 print(("F OREL F = ",  a(FALSE) OREL  b(FALSE), new line));
 print(("F OREL T = ",  a(FALSE) OREL  b(TRUE), new line));

 print(("T ANDTH F = ", a(TRUE) ANDTH b(FALSE), new line));
 print(("T ANDTH T = ", a(TRUE) ANDTH b(TRUE), new line))

CO;

Valid for Algol 68G and 68C using non standard operators #

 print(("T ORF F = ", a(TRUE) ORF b(FALSE), new line));
 print(("F ANDF T = ", a(FALSE) ANDF b(TRUE), new line))

END CO

)</lang>

Output:

a=T, T OREL F = T
a=T, T OREL T = T
a=F, F ANDTH F = F
a=F, F ANDTH T = F
a=F, b=F, F OREL F = F
a=F, b=T, F OREL T = T
a=T, b=F, T ANDTH F = F
a=T, b=T, T ANDTH T = T

ALGOL W

In Algol W the boolean "and" and "or" operators are short circuit operators. <lang algolw>begin

   logical procedure a( logical value v ) ; begin write( "a: ", v ); v end ;
   logical procedure b( logical value v ) ; begin write( "b: ", v ); v end ;

   write( "and: ", a( true  ) and b( true ) );
   write( "---" );
   write( "or:  ", a( true  ) or  b( true ) );
   write( "---" );
   write( "and: ", a( false ) and b( true ) );
   write( "---" );
   write( "or:  ", a( false ) or  b( true ) );
   write( "---" );

end.</lang>

Output:

and: 
a:   true  
b:   true    true  
---
or:  
a:   true    true  
---
and: 
a:  false   false  
---
or:  
a:  false  
b:   true    true  
---

AppleScript

AppleScript's boolean operators are short-circuiting (as can be seen from the log below).

What AppleScript lacks, however, is a short-circuiting ternary operator like the e ? e2 : e3 of C, or a short-circuiting three-argument function like cond in Lisp. To get a similar effect in AppleScript, we have to delay evaluation on both sides, using a cond which returns a reference to one of two unapplied handlers, and composing the result with a separate apply function, to apply the selected handler function to its argument.

(As a statement, rather than an expression, the if ... then ... else structure does not compose – unlike cond or ? :, it can not be nested inside expressions)

<lang AppleScript>on run

   map(test, {|and|, |or|})

end run

-- test :: ((Bool, Bool) -> Bool) -> (Bool, Bool, Bool, Bool) on test(f)

   map(f, {{true, true}, {true, false}, {false, true}, {false, false}})

end test

-- |and| :: (Bool, Bool) -> Bool on |and|(tuple)

   set {x, y} to tuple
   
   a(x) and b(y)

end |and|

-- |or| :: (Bool, Bool) -> Bool on |or|(tuple)

   set {x, y} to tuple
   
   a(x) or b(y)

end |or|

-- a :: Bool -> Bool on a(bool)

   log "a"
   return bool

end a

-- b :: Bool -> Bool on b(bool)

   log "b"
   return bool

end b

-- map :: (a -> b) -> [a] -> [b] on map(f, xs)

   script mf
       property lambda : f
   end script
   set lng to length of xs
   set lst to {}
   repeat with i from 1 to lng
       set end of lst to mf's lambda(item i of xs, i, xs)
   end repeat
   return lst

end map

</lang>

Output:

Messages:
(*a*)
(*b*)
(*a*)
(*b*)
(*a*)
(*a*)
(*a*)
(*a*)
(*a*)
(*b*)
(*a*)
(*b*)
Result:
{{true, false, false, false}, {true, true, true, false}}

AutoHotkey

In AutoHotkey, the boolean operators, and, or, and ternaries, short-circuit: <lang AutoHotkey>i = 1 j = 1 x := a(i) and b(j) y := a(i) or b(j)

a(p) {

MsgBox, a() was called with the parameter "%p%".
Return, p

}

b(p) {

MsgBox, b() was called with the parameter "%p%".
Return, p

}</lang>

AWK

Short-circuit evalation is done in logical AND (&&) and logical OR (||) operators: <lang AWK>#!/usr/bin/awk -f BEGIN { print (a(1) && b(1)) print (a(1) || b(1)) print (a(0) && b(1)) print (a(0) || b(1)) }

function a(x) { print " x:"x return x } function b(y) { print " y:"y return y }</lang>

Output:

  x:1
  y:1
1
  x:1
1
  x:0
0
  x:0
  y:1
1

Axe

<lang axe>TEST(0,0) TEST(0,1) TEST(1,0) TEST(1,1) Return

Lbl TEST r₁→X r₂→Y Disp X▶Hex+3," and ",Y▶Hex+3," = ",(A(X)?B(Y))▶Hex+3,i Disp X▶Hex+3," or ",Y▶Hex+3," = ",(A(X)??B(Y))▶Hex+3,i .Wait for keypress getKeyʳ Return

Lbl A r₁ Return

Lbl B r₁ Return</lang>

BaCon

BaCon supports short-circuit evaluation.

<lang freebasic>' Short-circuit evaluation FUNCTION a(f)

   PRINT "FUNCTION a"
   RETURN f

END FUNCTION

FUNCTION b(f)

   PRINT "FUNCTION b"
   RETURN f

END FUNCTION

PRINT "FALSE and TRUE" x = a(FALSE) AND b(TRUE) PRINT x

PRINT "TRUE and TRUE" x = a(TRUE) AND b(TRUE) PRINT x

PRINT "FALSE or FALSE" y = a(FALSE) OR b(FALSE) PRINT y

PRINT "TRUE or FALSE" y = a(TRUE) OR b(FALSE) PRINT y</lang>

Output:

prompt$ ./short-circuit
FALSE and TRUE
FUNCTION a
0
TRUE and TRUE
FUNCTION a
FUNCTION b
1
FALSE or FALSE
FUNCTION a
FUNCTION b
0
TRUE or FALSE
FUNCTION a
1

Batch File

Translation of: Liberty BASIC

<lang dos>%=== Batch Files have no booleans. ===% %=== I will instead use 1 as true and 0 as false. ===%

@echo off setlocal enabledelayedexpansion echo AND for /l %%i in (0,1,1) do ( for /l %%j in (0,1,1) do ( echo.a^(%%i^) AND b^(%%j^) call :a %%i set res=!bool_a! if not !res!==0 ( call :b %%j set res=!bool_b! ) echo.=^> !res! ) )

echo --------------------------------- echo OR for /l %%i in (0,1,1) do ( for /l %%j in (0,1,1) do ( echo a^(%%i^) OR b^(%%j^) call :a %%i set res=!bool_a! if !res!==0 ( call :b %%j set res=!bool_b! ) echo.=^> !res! ) ) pause>nul exit /b 0

----------------------------------------

a

echo. calls func a set bool_a=%1 goto :EOF

b

echo. calls func b set bool_b=%1 goto :EOF</lang>

Output:

AND
a(0) AND b(0)
        calls func a
=>      0
a(0) AND b(1)
        calls func a
=>      0
a(1) AND b(0)
        calls func a
        calls func b
=>      0
a(1) AND b(1)
        calls func a
        calls func b
=>      1
---------------------------------
OR
a(0) OR b(0)
        calls func a
        calls func b
=>      0
a(0) OR b(1)
        calls func a
        calls func b
=>      1
a(1) OR b(0)
        calls func a
=>      1
a(1) OR b(1)
        calls func a
=>      1

BBC BASIC

Short-circuit operators aren't implemented directly, but short-circuit AND can be simulated using cascaded IFs. Short-circuit OR can be converted into a short-circuit AND using De Morgan's laws. <lang bbcbasic> REM TRUE is represented as -1, FALSE as 0

     FOR i% = TRUE TO FALSE
       FOR j% = TRUE TO FALSE
         PRINT "For x=a(";FNboolstring(i%);") AND b(";FNboolstring(j%);")"
         x% = FALSE
         REM Short-circuit AND can be simulated by cascaded IFs:
         IF FNa(i%) IF FNb(j%) THEN x%=TRUE
         PRINT "x is ";FNboolstring(x%)
         PRINT
         PRINT "For y=a(";FNboolstring(i%);") OR b(";FNboolstring(j%);")"
         y% = FALSE
         REM Short-circuit OR can be simulated by De Morgan's laws:
         IF NOTFNa(i%) IF NOTFNb(j%) ELSE y%=TRUE : REM Note ELSE without THEN
         PRINT "y is ";FNboolstring(y%)
         PRINT
       NEXT:NEXT
     END
     
     DEFFNa(bool%)
     PRINT "Function A used; ";
     =bool%
     
     DEFFNb(bool%)
     PRINT "Function B used; ";
     =bool%
     
     DEFFNboolstring(bool%)
     IF bool%=0 THEN ="FALSE" ELSE="TRUE"</lang>

This gives the results shown below:

For x=a(TRUE) AND b(TRUE)
Function A used; Function B used; x is TRUE

For y=a(TRUE) OR b(TRUE)
Function A used; y is TRUE

For x=a(TRUE) AND b(FALSE)
Function A used; Function B used; x is FALSE

For y=a(TRUE) OR b(FALSE)
Function A used; y is TRUE

For x=a(FALSE) AND b(TRUE)
Function A used; x is FALSE

For y=a(FALSE) OR b(TRUE)
Function A used; Function B used; y is TRUE

For x=a(FALSE) AND b(FALSE)
Function A used; x is FALSE

For y=a(FALSE) OR b(FALSE)
Function A used; Function B used; y is FALSE

Bracmat

Bracmat has no booleans. The closest thing is the success or failure of an expression. A function is not called if the argument fails, so we have to use a trick to pass 'failure' to a function. Here it is accomplished by an extra level of indirection: two == in the definition of 'false' (and 'true', for symmetry) and two !! when evaluating the argument in the functions a and b. The backtick is another hack. This prefix tells Bracmat to look the other way if the backticked expression fails and to continue as if the expression succeeded. A neater way is to introduce an extra OR operator. That solution would have obscured the core of the current task. Short-circuit evaluation is heavily used in Bracmat code. Although not required, it is a good habit to exclusively use AND (&) and OR (|) operators to separate expressions, as the code below exemplifies. <lang bracmat>( (a=.out$"I'm a"&!!arg) & (b=.out$"I'm b"&!!arg) & (false==~) & (true==) & !false !true:?outer & whl

 ' ( !outer:%?x ?outer
   & !false !true:?inner
   &   whl
     ' ( !inner:%?y ?inner
       &   out
         $ ( Testing
             (!!x&true|false)
             AND
             (!!y&true|false)
           )
       & `(a$!x&b$!y)
       &   out
         $ ( Testing
             (!!x&true|false)
             OR
             (!!y&true|false)
           )
       & `(a$!x|b$!y)
       )
   )

& done ); </lang> Output:

Testing false AND false
I'm a
Testing false OR false
I'm a
I'm b
Testing false AND true
I'm a
Testing false OR true
I'm a
I'm b
Testing true AND false
I'm a
I'm b
Testing true OR false
I'm a
Testing true AND true
I'm a
I'm b
Testing true OR true
I'm a

C

Boolean operators && and || are shortcircuit operators. <lang c>#include <stdio.h>

include <stdbool.h>

bool a(bool in) {

 printf("I am a\n");
 return in;

}

bool b(bool in) {

 printf("I am b\n");
 return in;

}

define TEST(X,Y,O) \

 do {								\
   x = a(X) O b(Y);						\
   printf(#X " " #O " " #Y " = %s\n\n", x ? "true" : "false");	\
 } while(false);

int main() {

 bool x;

 TEST(false, true, &&); // b is not evaluated
 TEST(true, false, ||); // b is not evaluated
 TEST(true, false, &&); // b is evaluated
 TEST(false, false, ||); // b is evaluated

 return 0;

}</lang>

C#

<lang csharp>using System;

class Program {

   static bool a(bool value)
   {
       Console.WriteLine("a");
       return value;
   }

   static bool b(bool value)
   {
       Console.WriteLine("b");
       return value;
   }

   static void Main()
   {
       foreach (var i in new[] { false, true })
       {
           foreach (var j in new[] { false, true })
           {
               Console.WriteLine("{0} and {1} = {2}", i, j, a(i) && b(j));
               Console.WriteLine();
               Console.WriteLine("{0} or {1} = {2}", i, j, a(i) || b(j));
               Console.WriteLine();
           }
       }
   }

}</lang>

Output:

<lang>a False and False = False

a b False or False = False

a False and True = False

a b False or True = True

a b True and False = False

a True or False = True

a b True and True = True

a True or True = True</lang>

C++

Just like C, boolean operators && and || are shortcircuit operators. <lang cpp>#include <iostream>

bool a(bool in) {

   std::cout << "a" << std::endl;
   return in;

}

bool b(bool in) {

   std::cout << "b" << std::endl;
   return in;

}

void test(bool i, bool j) {

   std::cout << std::boolalpha << i << " and " << j << " = " << (a(i) && b(j)) << std::endl;
   std::cout << std::boolalpha << i << " or " << j << " = " << (a(i) || b(j)) << std::endl;

}

int main() {

   test(false, false);
   test(false, true);
   test(true, false);
   test(true, true);
   return 0;

}</lang>

Output:

a 
false and false = false
a 
b 
false or false = false
a 
false and true = false
a 
b 
false or true = true
a 
b 
true and false = false
a 
true or false = true
a 
b 
true and true = true
a 
true or true = true

Clojure

The print/println stuff in the doseq is kinda gross, but if you include them all in a single print, then the function traces are printed before the rest (since it has to evaluate them before calling print). <lang Clojure>(letfn [(a [bool] (print "(a)") bool)

       (b [bool] (print "(b)") bool)]  
 (doseq [i [true false] j [true false]]
   (print i "OR" j "= ")               
   (println (or (a i) (b j)))          
   (print i "AND" j " = ")             
   (println (and (a i) (b j)))))</lang>

Output:

true OR true = (a)true       
true AND true  = (a)(b)true  
true OR false = (a)true      
true AND false  = (a)(b)false
false OR true = (a)(b)true   
false AND true  = (a)false   
false OR false = (a)(b)false 
false AND false  = (a)false

Common Lisp

<lang lisp>(defun a (F)

    (print 'a)
    F )

(defun b (F)

    (print 'b)
    F )

(dolist (x '((nil nil) (nil T) (T T) (T nil)))

       (format t "~%(and ~S)" x) 
       (and (a (car x)) (b (car(cdr x)))) 
       (format t "~%(or ~S)" x) 
       (or (a (car x)) (b (car(cdr x)))))</lang>

Output:

(and (NIL NIL))
A 
(or (NIL NIL))
A 
B 
(and (NIL T))
A 
(or (NIL T))
A 
B 
(and (T T))
A 
B 
(or (T T))
A 
(and (T NIL))
A 
B 
(or (T NIL))
A

D

Translation of: Python

<lang d>import std.stdio, std.algorithm;

T a(T)(T answer) {

   writefln("  # Called function a(%s) -> %s", answer, answer);
   return answer;

}

T b(T)(T answer) {

   writefln("  # Called function b(%s) -> %s", answer, answer);
   return answer;

}

void main() {

   foreach (immutable x, immutable y;
            [false, true].cartesianProduct([false, true])) {
       writeln("\nCalculating: r1 = a(x) && b(y)");
       immutable r1 = a(x) && b(y);
       writeln("Calculating: r2 = a(x) || b(y)");
       immutable r2 = a(x) || b(y);
   }

}</lang>

Output:

Calculating: r1 = a(x) && b(y)
  # Called function a(false) -> false
Calculating: r2 = a(x) || b(y)
  # Called function a(false) -> false
  # Called function b(false) -> false

Calculating: r1 = a(x) && b(y)
  # Called function a(true) -> true
  # Called function b(false) -> false
Calculating: r2 = a(x) || b(y)
  # Called function a(true) -> true

Calculating: r1 = a(x) && b(y)
  # Called function a(false) -> false
Calculating: r2 = a(x) || b(y)
  # Called function a(false) -> false
  # Called function b(true) -> true

Calculating: r1 = a(x) && b(y)
  # Called function a(true) -> true
  # Called function b(true) -> true
Calculating: r2 = a(x) || b(y)
  # Called function a(true) -> true

Delphi

Delphi supports short circuit evaluation by default. It can be turned off using the {$BOOLEVAL OFF} compiler directive. <lang Delphi>program ShortCircuitEvaluation;

{$APPTYPE CONSOLE}

uses SysUtils;

function A(aValue: Boolean): Boolean; begin

 Writeln('a');
 Result := aValue;

end;

function B(aValue: Boolean): Boolean; begin

 Writeln('b');
 Result := aValue;

end;

var

 i, j: Boolean;

begin

 for i in [False, True] do
 begin
   for j in [False, True] do
   begin
     Writeln(Format('%s and %s = %s', [BoolToStr(i, True), BoolToStr(j, True), BoolToStr(A(i) and B(j), True)]));
     Writeln;
     Writeln(Format('%s or %s = %s', [BoolToStr(i, True), BoolToStr(j, True), BoolToStr(A(i) or B(j), True)]));
     Writeln;
   end;
 end;

end.</lang>

Dyalect

Translation of: Swift

<lang dyalect>func a(v) {

   print(nameof(a), terminator: "")
   return v

}

func b(v) {

   print(nameof(b), terminator: "")
   return v

}

func test(i, j) {

   print("Testing a(\(i)) && b(\(j))")
   print("Trace: ", terminator: "")
   print("\nResult: \(a(i) && b(j))")

   print("Testing a(\(i)) || b(\(j))")
   print("Trace: ", terminator: "")
   print("\nResult: \(a(i) || b(j))")

   print()

}

test(false, false) test(false, true) test(true, false) test(true, true)</lang>

Output:

Testing a(false) && b(false)
Trace: a
Result: false
Testing a(false) || b(false)
Trace: ab
Result: false

Testing a(false) && b(true)
Trace: a
Result: false
Testing a(false) || b(true)
Trace: ab
Result: true

Testing a(true) && b(false)
Trace: ab
Result: false
Testing a(true) || b(false)
Trace: a
Result: true

Testing a(true) && b(true)
Trace: ab
Result: true
Testing a(true) || b(true)
Trace: a
Result: true

E

E defines && and || in the usual short-circuiting fashion. <lang e>def a(v) { println("a"); return v } def b(v) { println("b"); return v }

def x := a(i) && b(j) def y := b(i) || b(j)</lang> Unusually, E is an expression-oriented language, and variable bindings (which are expressions) are in scope until the end of the nearest enclosing { ... } block. The combination of these features means that some semantics must be given to a binding occurring inside of a short-circuited alternative. <lang e>def x := a(i) && (def funky := b(j))</lang> The choice we make is that funky is ordinary if the right-side expression was evaluated, and otherwise is ruined; attempts to access the variable give an error.

Elena

ELENA 5.0 : <lang elena>import system'routines; import extensions;

Func<bool, bool> a = (bool x){ console.writeLine:"a"; ^ x };

Func<bool, bool> b = (bool x){ console.writeLine:"b"; ^ x };

const bool[] boolValues = new bool[]{ false, true };

public program() {

   boolValues.forEach:(bool i)
   {
       boolValues.forEach:(bool j)
       {
           console.printLine(i," and ",j," = ",a(i) && b(j));

           console.writeLine();
           console.printLine(i," or ",j," = ",a(i) || b(j));
           console.writeLine()
       }
   }

}</lang>

Output:

a
false and false = false

a
b
false or false = false

a
false and true = false

a
b
false or true = true

a
b
true and false = false

a
true or false = true

a
b
true and true = true

a
true or true = true

Elixir

<lang elixir>defmodule Short_circuit do

 defp a(bool) do
   IO.puts "a( #{bool} ) called"
   bool
 end
 
 defp b(bool) do
   IO.puts "b( #{bool} ) called"
   bool
 end
 
 def task do
   Enum.each([true, false], fn i ->
     Enum.each([true, false], fn j ->
       IO.puts "a( #{i} ) and b( #{j} ) is #{a(i) and b(j)}.\n"
       IO.puts "a( #{i} ) or b( #{j} ) is #{a(i)  or b(j)}.\n"
     end)
   end)
 end

end

Short_circuit.task</lang>

Output:

a( true ) called
b( true ) called
a( true ) and b( true ) is true.

a( true ) called
a( true ) or b( true ) is true.

a( true ) called
b( false ) called
a( true ) and b( false ) is false.

a( true ) called
a( true ) or b( false ) is true.

a( false ) called
a( false ) and b( true ) is false.

a( false ) called
b( true ) called
a( false ) or b( true ) is true.

a( false ) called
a( false ) and b( false ) is false.

a( false ) called
b( false ) called
a( false ) or b( false ) is false.

Erlang

<lang Erlang> -module( short_circuit_evaluation ).

-export( [task/0] ).

task() -> [task_helper(X, Y) || X <- [true, false], Y <- [true, false]].

a( Boolean ) -> io:fwrite( " a ~p~n", [Boolean] ), Boolean.

b( Boolean ) -> io:fwrite( " b ~p~n", [Boolean] ), Boolean.

task_helper( Boolean1, Boolean2 ) -> io:fwrite( "~p andalso ~p~n", [Boolean1, Boolean2] ), io:fwrite( "=> ~p~n", [a(Boolean1) andalso b(Boolean2)] ), io:fwrite( "~p orelse ~p~n", [Boolean1, Boolean2] ), io:fwrite( "=> ~p~n", [a(Boolean1) orelse b(Boolean2)] ). </lang>

Output:

15> short_circuit_evaluation:task().
true andalso true
 a true
 b true
=> true
true orelse true
 a true
=> true
true andalso false
 a true
 b false
=> false
true orelse false
 a true
=> true
false andalso true
 a false
=> false
false orelse true
 a false
 b true
=> true
false andalso false
 a false
=> false
false orelse false
 a false
 b false
=> false

F#

<lang fsharp>let a (x : bool) = printf "(a)"; x let b (x : bool) = printf "(b)"; x

[for x in [true; false] do for y in [true; false] do yield (x, y)] |> List.iter (fun (x, y) ->

   printfn "%b AND %b = %b" x y ((a x) && (b y))
   printfn "%b OR %b = %b" x y ((a x) || (b y)))</lang>

Output

(a)(b)true AND true = true
(a)true OR true = true
(a)(b)true AND false = false
(a)true OR false = true
(a)false AND true = false
(a)(b)false OR true = true
(a)false AND false = false
(a)(b)false OR false = false

Factor

&& and || perform short-circuit evaluation, while and and or do not. && and || both expect a sequence of quotations to evaluate in a short-circuit manner. They are smart combinators; that is, they infer the number of arguments taken by the quotations. If you opt not to use the smart combinators, you can also use words like 0&& and 2|| where the arity of the quotations is dictated. <lang factor>USING: combinators.short-circuit.smart io prettyprint ; IN: rosetta-code.short-circuit

a ( ? -- ? ) "(a)" write ;

b ( ? -- ? ) "(b)" write ;

"f && f = " write { [ f a ] [ f b ] } && . "f || f = " write { [ f a ] [ f b ] } || . "f && t = " write { [ f a ] [ t b ] } && . "f || t = " write { [ f a ] [ t b ] } || . "t && f = " write { [ t a ] [ f b ] } && . "t || f = " write { [ t a ] [ f b ] } || . "t && t = " write { [ t a ] [ t b ] } && . "t || t = " write { [ t a ] [ t b ] } || .</lang>

Output:

f && f = (a)f
f || f = (a)(b)f
f && t = (a)f
f || t = (a)(b)t
t && f = (a)(b)f
t || f = (a)t
t && t = (a)(b)t
t || t = (a)t

Fantom

<lang fantom>class Main {

 static Bool a (Bool value)
 {
   echo ("in a")
   return value
 }

 static Bool b (Bool value)
 {
   echo ("in b")
   return value
 }

 public static Void main ()
 {
   [false,true].each |i|
   {
     [false,true].each |j|
     {
       Bool result := a(i) && b(j)
       echo ("a($i) && b($j): " + result)
       result = a(i) || b(j)
       echo ("a($i) || b($j): " + result)
     }
   }
 }

}</lang>

Output:

in a
a(false) && b(false): false
in a
in b
a(false) || b(false): false
in a
a(false) && b(true): false
in a
in b
a(false) || b(true): true
in a
in b
a(true) && b(false): false
in a
a(true) || b(false): true
in a
in b
a(true) && b(true): true
in a
a(true) || b(true): true

Forth

<lang forth>\ Short-circuit evaluation definitions from Wil Baden, with minor name changes

ENDIF postpone THEN ; immediate

COND 0 ; immediate

ENDIFS BEGIN DUP WHILE postpone ENDIF REPEAT DROP ; immediate

ORELSE s" ?DUP 0= IF" evaluate ; immediate

ANDIF s" DUP IF DROP" evaluate ; immediate

.bool IF ." true " ELSE ." false " THEN ;

A ." A=" DUP .bool ;

B ." B=" DUP .bool ;

test

 CR
 1 -1 DO 1 -1 DO
   COND I A ANDIF  J B ENDIFS ." ANDIF="  .bool CR
   COND I A ORELSE J B ENDIFS ." ORELSE=" .bool CR
 LOOP LOOP ;

\ An alternative based on explicitly short-circuiting conditionals, Dave Keenan

END-PRIOR-IF 1 CS-ROLL postpone ENDIF ; immediate

test

 CR
 1 -1 DO 1 -1 DO
   I A    IF J B IF 1 ELSE END-PRIOR-IF 0 ENDIF ." ANDIF="  .bool CR
   I A 0= IF J B IF END-PRIOR-IF 1 ELSE 0 ENDIF ." ORELSE=" .bool CR
 LOOP LOOP ;</lang>

Output:

A=true  B=true  ANDIF=true
A=true  ORELSE=true
A=false ANDIF=false
A=false B=true  ORELSE=true
A=true  B=false ANDIF=false
A=true  ORELSE=true
A=false ANDIF=false
A=false B=false ORELSE=false

Fortran

Works with: Fortran version 90 and later

Using an IF .. THEN .. ELSE construct <lang fortran>program Short_Circuit_Eval

 implicit none

 logical :: x, y
 logical, dimension(2) :: l = (/ .false., .true. /)
 integer :: i, j

 do i = 1, 2
   do j = 1, 2
     write(*, "(a,l1,a,l1,a)") "Calculating x = a(", l(i), ") and b(", l(j), ")"   
     ! a AND b
     x = a(l(i))  
     if(x) then
       x = b(l(j))
       write(*, "(a,l1)") "x = ", x
     else
       write(*, "(a,l1)") "x = ", x
     end if
 
     write(*,*)
     write(*, "(a,l1,a,l1,a)") "Calculating y = a(", l(i), ") or b(", l(j), ")"   
     ! a OR b
     y = a(l(i))
     if(y) then
       write(*, "(a,l1)") "y = ", y
     else
       y = b(l(j))
       write(*, "(a,l1)") "y = ", y
     end if
     write(*,*)
   end do
 end do

contains

function a(value)

 logical :: a
 logical, intent(in) :: value

 a = value
 write(*, "(a,l1,a)") "Called function a(", value, ")"

end function

function b(value)

 logical :: b
 logical, intent(in) :: value
 
 b = value
 write(*, "(a,l1,a)") "Called function b(", value, ")"

end function end program</lang>

Output:

Calculating x = a(F) and b(F)
Called function a(F)
x = F
 
Calculating y = a(F) or b(F)
Called function a(F)
Called function b(F)
y = F
 
Calculating x = a(F) and b(T)
Called function a(F)
x = F
 
Calculating y = a(F) or b(T)
Called function a(F)
Called function b(T)
y = T
 
Calculating x = a(T) and b(F)
Called function a(T)
Called function b(F)
x = F
 
Calculating y = a(T) or b(F)
Called function a(T)
y = T
 
Calculating x = a(T) and b(T)
Called function a(T)
Called function b(T)
x = T
 
Calculating y = a(T) or b(T)
Called function a(T)
y = T

FreeBASIC

<lang freebasic>' FB 1.05.0 Win64

Function a(p As Boolean) As Boolean

 Print "a() called"
 Return p

End Function

Function b(p As Boolean) As Boolean

 Print "b() called"
 Return p

End Function

Dim As Boolean i, j, x, y i = False j = True Print "Without short-circuit evaluation :" Print x = a(i) And b(j) y = a(i) Or b(j) Print "x = "; x; " y = "; y Print Print "With short-circuit evaluation :" Print x = a(i) AndAlso b(j) b(j) not called as a(i) = false and so x must be false y = a(i) OrElse b(j) b(j) still called as can't determine y unless it is Print "x = "; x; " y = "; y Print Print "Press any key to quit" Sleep</lang>

Output:

Without short-circuit evaluation :

a() called
b() called
a() called
b() called
x = false y = true

With short-circuit evaluation :

a() called
a() called
b() called
x = false y = true

Fōrmulæ

In this page you can see the solution of this task.

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

The option to show Fōrmulæ programs and their results is showing images. Unfortunately images cannot be uploaded in Rosetta Code.

Go

Short circuit operators are && and ||. <lang go>package main

import "fmt"

func a(v bool) bool {

   fmt.Print("a")
   return v

}

func b(v bool) bool {

   fmt.Print("b")
   return v

}

func test(i, j bool) {

   fmt.Printf("Testing a(%t) && b(%t)\n", i, j)
   fmt.Print("Trace:  ")
   fmt.Println("\nResult:", a(i) && b(j))

   fmt.Printf("Testing a(%t) || b(%t)\n", i, j)
   fmt.Print("Trace:  ")
   fmt.Println("\nResult:", a(i) || b(j))

   fmt.Println("")

}

func main() {

   test(false, false)
   test(false, true)
   test(true, false)
   test(true, true)

}</lang>

Output:

Testing a(false) && b(false)
Trace:  a
Result: false
Testing a(false) || b(false)
Trace:  ab
Result: false

Testing a(false) && b(true)
Trace:  a
Result: false
Testing a(false) || b(true)
Trace:  ab
Result: true

Testing a(true) && b(false)
Trace:  ab
Result: false
Testing a(true) || b(false)
Trace:  a
Result: true

Testing a(true) && b(true)
Trace:  ab
Result: true
Testing a(true) || b(true)
Trace:  a
Result: true

Groovy

Like all C-based languages (of which I am aware), Groovy short-circuits the logical and (&&) and logical or (||) operations, but not the bitwise and (&) and bitwise or (|) operations. <lang groovy>def f = { println ' AHA!'; it instanceof String } def g = { printf ('%5d ', it); it > 50 }

println 'bitwise' assert g(100) & f('sss') assert g(2) | f('sss') assert ! (g(1) & f('sss')) assert g(200) | f('sss')

println logical assert g(100) && f('sss') assert g(2) || f('sss') assert ! (g(1) && f('sss')) assert g(200) || f('sss')</lang>

Output:

bitwise
  100   AHA!
    2   AHA!
    1   AHA!
  200   AHA!

logical
  100   AHA!
    2   AHA!
    1   200

Haskell

Lazy evaluation makes it possible for user-defined functions to be short-circuited. An expression will not be evaluated as long as it is not pattern matched: <lang haskell>module ShortCircuit where

import Prelude hiding ((&&), (||)) import Debug.Trace

False && _ = False True && False = False _ && _ = True

True || _ = True False || True = True _ || _ = False

a p = trace ("<a " ++ show p ++ ">") p b p = trace ("") p

main = mapM_ print ( [ a p || b q | p <- [False, True], q <- [False, True] ]

++ [ a p && b q | p <- [False, True], q <- [False, True] ])</lang>

Output:
<a False> False <a False> True <a True> True <a True> True <a False> False <a False> False <a True> False <a True> True
One can force the right-hand arguemnt to be evaluated first be using the alternate definitions: <lang haskell>_ && False = False False && True = False _ && _ = True
_ || True = True True || False = True _ || _ = False</lang>

Output:
 <a False> False True <a True> True True False <a False> False False <a True> True
The order of evaluation (in this case the original order again) can be seen in a more explicit form by desugaring the pattern matching: <lang haskell>p && q = case p of
False -> False _ -> case q of False -> False _ -> True
p || q = case p of
True -> True _ -> case q of True -> True _ -> False</lang>
Icon and Unicon
The entire concept of using 'boolean' values for logic control runs counter to the philosophy of Icon. Instead Icon has success (something that returns a result) and failure which is really a signal. The concept is similar to that used in SNOBOL4 and Lisp and far more potent than passing around and testing booleans. There is no way to pass around a 'false' value in that sense. Icon does have facilities for dealing with bits inside integers but these would not normally be used for control purposes. Because failure is a signal control is always evaluated in a short-circuit manner. One consequence of this is that an expression "i < j" doesn't return a boolean value, instead it returns the value of j. While this may seem odd at first it allows for elegant expressions like "i < j < k". Another benefit is that there is no need for programmers to devote effort to staying inside the bounds of any data type. For instance, if you loop and iterate beyond bounds the expression simply fails and the loop ends.
While this task could be written literally, it would be more beneficial to show how an Icon programmer would approach the same problem. Icon extends the idea short circuit evaluation with the ability for expressions to generate alternate results only if needed. For more information see Failure is an option, Everything Returns a Value Except when it Doesn't, and Goal-Directed Evaluation and Generators. Consequently some small liberties will be taken with this task:
Since any result means an expression succeeded and is hence true, we can use any value. In this example our choice will be determined by how we deal with 'false'.

The inability to pass a 'false' value is a challenge. At first glance we might try &null, similar to Lisp, but there is no canonical true. Also &null produces a result, so strictly speaking it could be 'true' as well. A good example of this is that an expression like " not expr " returns null if 'expr' fails.

For this example we will define two procedures 'true' and 'false'. Because Icon treats procedures as a data type we can assign them and invoke them indirectly via the variable name they are assigned to. We can write " i := true " and later invoke 'true' via " i() ".

Rather than have the tasks print their own name, we will just utilize built-in tracing which will be more informative.
This use of procedures as values is somewhat contrived but serves us well for demonstration purposes. In practice this approach would be strained since failure results aren't re-captured as values (and can't easily be). <lang Icon>procedure main() &trace := -1 # ensures functions print their names
every (i := false | true ) & ( j := false | true) do {
write("i,j := ",image(i),", ",image(j)) write("i & j:") x := i() & j() # invoke true/false write("i | j:") y := i() | j() # invoke true/false }
end
procedure true() #: succeeds always (returning null) return end
procedure false() #: fails always fail # for clarity but not needed as running into end has the same effect end</lang>

Sample output for a single case:

i,j := procedure true, procedure false i & j: Shortcircuit.icn: 8 | true() Shortcircuit.icn: 16 | true returned &null Shortcircuit.icn: 8 | false() Shortcircuit.icn: 20 | false failed i | j: Shortcircuit.icn: 10 | true() Shortcircuit.icn: 16 | true returned &null i,j := procedure true, procedure true
Io
Translation of: Ruby
<lang Io>a := method(bool,
writeln("a(#{bool}) called." interpolate) bool
) b := method(bool,
writeln("b(#{bool}) called." interpolate) bool
)
list(true,false) foreach(avalue,
list(true,false) foreach(bvalue, x := a(avalue) and b(bvalue) writeln("x = a(#{avalue}) and b(#{bvalue}) is #{x}" interpolate) writeln y := a(avalue) or b(bvalue) writeln("y = a(#{avalue}) or b(#{bvalue}) is #{y}" interpolate) writeln )
)</lang>

Output:
a(true) called. b(true) called. x = a(true) and b(true) is true a(true) called. y = a(true) or b(true) is true a(true) called. b(false) called. x = a(true) and b(false) is false a(true) called. y = a(true) or b(false) is true a(false) called. x = a(false) and b(true) is false a(false) called. b(true) called. y = a(false) or b(true) is true a(false) called. x = a(false) and b(false) is false a(false) called. b(false) called. y = a(false) or b(false) is false
J
See the J wiki entry on short circuit booleans. <lang j>labeled=:1 :'[ smoutput@,&":~&m' A=: 'A ' labeled B=: 'B ' labeled and=: ^: or=: 2 :'u^:(-.@v)'</lang>

Example:
<lang j> (A and B) 1 B 1 A 1 1
(A and B) 0
B 0 0
(A or B) 1
B 1 1
(A or B) 0
B 0 A 0 0</lang> Note that J evaluates right-to-left.
Note also that both functions take the same argument (which might make this less than ideal for some purposes, but trying micromanage flow of control is usually counter-productive in J in much the way that global values can be counter-productive in an object oriented environment. When you are processing a large set of array data, flow of control can only make sense when it is relevant to all of the data being processed -- if you want to manage flow of control which is not relevant to the entire set of data being processed you might artificially reduce the amount of data being processed, along the lines of an SQL cursor).
Java
In Java the boolean operators && and || are short circuit operators. The eager operator counterparts are & and |. <lang java>public class ShortCirc {
public static void main(String[] args){ System.out.println("F and F = " + (a(false) && b(false)) + "\n"); System.out.println("F or F = " + (a(false) || b(false)) + "\n");
System.out.println("F and T = " + (a(false) && b(true)) + "\n"); System.out.println("F or T = " + (a(false) || b(true)) + "\n");
System.out.println("T and F = " + (a(true) && b(false)) + "\n"); System.out.println("T or F = " + (a(true) || b(false)) + "\n");
System.out.println("T and T = " + (a(true) && b(true)) + "\n"); System.out.println("T or T = " + (a(true) || b(true)) + "\n"); }
public static boolean a(boolean a){ System.out.println("a"); return a; }
public static boolean b(boolean b){ System.out.println("b"); return b; }
}</lang>

Output:
a F and F = false a b F or F = false a F and T = false a b F or T = true a b T and F = false a T or F = true a b T and T = true a T or T = true
JavaScript
Short-circuiting evaluation of boolean expressions has been the default since the first versions of JavaScript.
<lang JavaScript>(function () {
'use strict';
function a(bool) { console.log('a -->', bool);
return bool; }
function b(bool) { console.log('b -->', bool);
return bool; } var x = a(false) && b(true), y = a(true) || b(false), z = true ? a(true) : b(false); return [x, y, z];
})();</lang>
The console log shows that in each case (the binding of all three values), only the left-hand part of the expression (the application of a(expr)) was evaluated – b(expr) was skipped by logical short-circuiting.

Output:
Console:
/* a --> false */ /* a --> true */ /* a --> true */
Return value:
[false, true, true]
jq
jq's 'and' and 'or' are short-circuit operators. The following demonstration, which follows the "awk" example above, requires a version of jq with the built-in filter 'stderr'. <lang jq>def a(x): " a(\(x))" | stderr | x;
def b(y): " b(\(y))" | stderr | y;
"and:", (a(true) and b(true)), "or:", (a(true) or b(true)), "and:", (a(false) and b(true)), "or:", (a(false) or b(true))</lang>

Output:
<lang sh>$ jq -r -n -f Short-circuit-evaluation.jq and: " a(true)" " b(true)" true or: " a(true)" true and: " a(false)" false or: " a(false)" " b(true)" true</lang>
Julia
Julia does have short-circuit evaluation, which works just as you expect it to:
<lang julia>a(x) = (println("\t# Called a($x)"); return x) b(x) = (println("\t# Called b($x)"); return x)
for i in [true,false], j in [true, false]
println("\nCalculating: x = a($i) && b($j)"); x = a(i) && b(j) println("\tResult: x = $x") println("\nCalculating: y = a($i) || b($j)"); y = a(i) || b(j) println("\tResult: y = $y")
end</lang>

Output:
Calculating: x = a(true) && b(true) # Called a(true) # Called b(true) Result: x = true Calculating: y = a(true) || b(true) # Called a(true) Result: y = true Calculating: x = a(true) && b(false) # Called a(true) # Called b(false) Result: x = false Calculating: y = a(true) || b(false) # Called a(true) Result: y = true Calculating: x = a(false) && b(true) # Called a(false) Result: x = false Calculating: y = a(false) || b(true) # Called a(false) # Called b(true) Result: y = true Calculating: x = a(false) && b(false) # Called a(false) Result: x = false Calculating: y = a(false) || b(false) # Called a(false) # Called b(false) Result: y = false
Kotlin
<lang scala>// version 1.1.2
fun a(v: Boolean): Boolean {
println("'a' called") return v
}
fun b(v: Boolean): Boolean {
println("'b' called") return v
}
fun main(args: Array<String>){
val pairs = arrayOf(Pair(true, true), Pair(true, false), Pair(false, true), Pair(false, false)) for (pair in pairs) { val x = a(pair.first) && b(pair.second) println("${pair.first} && ${pair.second} = $x") val y = a(pair.first) || b(pair.second) println("${pair.first} || ${pair.second} = $y") println() }
}</lang>

Output:
'a' called 'b' called true && true = true 'a' called true || true = true 'a' called 'b' called true && false = false 'a' called true || false = true 'a' called false && true = false 'a' called 'b' called false || true = true 'a' called false && false = false 'a' called 'b' called false || false = false
Lambdatalk
Short-circuiting evaluation of boolean expressions has been the default since the first versions of lambdatalk.
<lang scheme> {def A {lambda {:bool} :bool}} -> A {def B {lambda {:bool} :bool}} -> B
{and {A true} {B true}} -> true {and {A true} {B false}} -> false {and {A false} {B true}} -> false {and {A false} {B false}} -> false
{or {A true} {B true}} -> true {or {A true} {B false}} -> true {or {A false} {B true}} -> true {or {A false} {B false}} -> false </lang>
Some more words about short-circuit evaluation. Lambdatalk comes with the {if "bool" then "one" else "two"} special form where "one" or "two" are not evaluated until "bool" is. This behaviour prevents useless computing and allows recursive processes. For instance, the naïve fibonacci function quickly leads to extensive computings. <lang scheme>
{def fib
{lambda {:n} {if {< :n 2} then 1 else {+ {fib {- :n 1}} {fib {- :n 2}}}}}}
-> fib
1) Using the if special form:
{if true then {+ 1 2} else {fib 29}} -> 3 // {fib 29} is not evaluated
{if false then {+ 1 2} else {fib 29}} -> 832040 // {fib 29} is evaluated in 5847ms
2) The if special form can't be simply replaced by a pair:
{def when {P.new {+ 1 2} {fib 29}}} // inner expressions are {P.left {when}} -> 3 // both evaluated before {P.right {when}} -> 832040 // and we don't want that
3) We can delay evaluation using lambdas:
{def when
{P.new {lambda {} {+ 1 2}} // will return a lambda {lambda {} {fib 22}} }} // to be evaluated later
-> when {{P.left {when}}} -> 3 // lambdas are evaluated {{P.right {when}}} -> 832040 // after choice using {}
</lang>
Liberty BASIC
LB does not have short-circuit evaluation. Implemented with IFs. <lang lb>print "AND" for i = 0 to 1
for j = 0 to 1 print "a("; i; ") AND b( "; j; ")" res =a( i) 'call always if res <>0 then 'short circuit if 0 res = b( j) end if print "=>",res next
next
print "---------------------------------" print "OR" for i = 0 to 1
for j = 0 to 1 print "a("; i; ") OR b("; j; ")" res =a( i) 'call always if res = 0 then 'short circuit if <>0 res = b( j) end if print "=>", res next
next
'---------------------------------------- function a( t)
print ,"calls func a" a = t
end function
function b( t)
print ,"calls func b" b = t
end function </lang>

Output:
AND a(0) AND b( 0) calls func a => 0 a(0) AND b( 1) calls func a => 0 a(1) AND b( 0) calls func a calls func b => 0 a(1) AND b( 1) calls func a calls func b => 1 --------------------------------- OR a(0) OR b(0) calls func a calls func b => 0 a(0) OR b(1) calls func a calls func b => 1 a(1) OR b(0) calls func a => 1 a(1) OR b(1) calls func a => 1
LiveCode
Livecode uses short-circuit evaluation. <lang LiveCode>global outcome function a bool
put "a called with" && bool & cr after outcome return bool
end a function b bool
put "b called with" && bool & cr after outcome return bool
end b
on mouseUp
local tExp put empty into outcome repeat for each item op in "and,or" repeat for each item x in "true,false" put merge("a(x) op b(x)") into tExp put merge(tExp && "is " & tExp & "") & cr after outcome put merge("a(x) op b(not x)") into tExp put merge(tExp && "is " & tExp & "") & cr after outcome end repeat put cr after outcome end repeat put outcome
end mouseUp</lang>
Logo
The AND and OR predicates may take either expressions which are all evaluated beforehand, or lists which are short-circuit evaluated from left to right only until the overall value of the expression can be determined. <lang logo>and [notequal? :x 0] [1/:x > 3] (or [:x < 0] [:y < 0] [sqrt :x + sqrt :y < 3])</lang>
Lua
<lang lua>function a(i)
print "Function a(i) called." return i
end
function b(i)
print "Function b(i) called." return i
end
i = true x = a(i) and b(i); print "" y = a(i) or b(i); print ""
i = false x = a(i) and b(i); print "" y = a(i) or b(i)</lang>
Maple
Built-in short circuit evaluation <lang Maple>a := proc(bool) printf("a is called->%s\n", bool): return bool: end proc: b := proc(bool) printf("b is called->%s\n", bool): return bool: end proc: for i in [true, false] do for j in [true, false] do printf("calculating x := a(i) and b(j)\n"): x := a(i) and b(j): printf("calculating x := a(i) or b(j)\n"): y := a(i) or b(j): od: od:</lang>

Output:
calculating x := a(i) and b(j) a is called->true b is called->true calculating x := a(i) or b(j) a is called->true calculating x := a(i) and b(j) a is called->true b is called->false calculating x := a(i) or b(j) a is called->true calculating x := a(i) and b(j) a is called->false calculating x := a(i) or b(j) a is called->false b is called->true calculating x := a(i) and b(j) a is called->false calculating x := a(i) or b(j) a is called->false b is called->false
Mathematica
Mathematica has built-in short-circuit evaluation of logical expressions. <lang Mathematica>a[in_] := (Print["a"]; in) b[in_] := (Print["b"]; in)
a[False] && b[True] a[True] || b[False]</lang> Evaluation of the preceding code gives:
a False a True
Whereas evaluating this: <lang Mathematica>a[True] && b[False]</lang> Gives:
a b False
MATLAB / Octave
Short-circuit evalation is done in logical AND (&&) and logical OR (||) operators: <lang matlab> function x=a(x)
printf('a: %i\n',x); end; function x=b(x) printf('b: %i\n',x); end;
a(1) && b(1) a(0) && b(1) a(1) || b(1) a(0) || b(1)</lang>

Output:
<lang matlab> > a(1) && b(1);
a: 1 b: 1 > a(0) && b(1); a: 0 > a(1) || b(1); a: 1 > a(0) || b(1); a: 0 b: 1</lang>
Modula-2
<lang modula2>MODULE ShortCircuit; FROM FormatString IMPORT FormatString; FROM Terminal IMPORT WriteString,WriteLn,ReadChar;
PROCEDURE a(v : BOOLEAN) : BOOLEAN; VAR buf : ARRAY[0..63] OF CHAR; BEGIN
FormatString(" # Called function a(%b)\n", buf, v); WriteString(buf); RETURN v
END a;
PROCEDURE b(v : BOOLEAN) : BOOLEAN; VAR buf : ARRAY[0..63] OF CHAR; BEGIN
FormatString(" # Called function b(%b)\n", buf, v); WriteString(buf); RETURN v
END b;
PROCEDURE Print(x,y : BOOLEAN); VAR buf : ARRAY[0..63] OF CHAR; VAR temp : BOOLEAN; BEGIN
FormatString("a(%b) AND b(%b)\n", buf, x, y); WriteString(buf); temp := a(x) AND b(y);
FormatString("a(%b) OR b(%b)\n", buf, x, y); WriteString(buf); temp := a(x) OR b(y);
WriteLn;
END Print;
BEGIN
Print(FALSE,FALSE); Print(FALSE,TRUE); Print(TRUE,TRUE); Print(TRUE,FALSE); ReadChar
END ShortCircuit.</lang>
MUMPS
MUMPS evaluates every expression it encounters, so we have to use conditional statements to do a short circuiting of the expensive second task. <lang MUMPS>SSEVAL1(IN)
WRITE !,?10,$STACK($STACK,"PLACE") QUIT IN
SSEVAL2(IN)
WRITE !,?10,$STACK($STACK,"PLACE") QUIT IN
SSEVAL3
NEW Z WRITE "1 AND 1" SET Z=$$SSEVAL1(1) SET:Z Z=Z&$$SSEVAL2(1) WRITE !,$SELECT(Z:"TRUE",1:"FALSE") WRITE !!,"0 AND 1" SET Z=$$SSEVAL1(0) SET:Z Z=Z&$$SSEVAL2(1) WRITE !,$SELECT(Z:"TRUE",1:"FALSE") WRITE !!,"1 OR 1" SET Z=$$SSEVAL1(1) SET:'Z Z=Z!$$SSEVAL2(1) WRITE !,$SELECT(Z:"TRUE",1:"FALSE") WRITE !!,"0 OR 1" SET Z=$$SSEVAL1(0) SET:'Z Z=Z!$$SSEVAL2(1) WRITE !,$SELECT(Z:"TRUE",1:"FALSE") KILL Z QUIT</lang>

Output:
USER>D SSEVAL3^ROSETTA 1 AND 1 SSEVAL1+1^ROSETTA +3 SSEVAL2+1^ROSETTA +3 TRUE 0 AND 1 SSEVAL1+1^ROSETTA +3 FALSE 1 OR 1 SSEVAL1+1^ROSETTA +3 TRUE 0 OR 1 SSEVAL1+1^ROSETTA +3 SSEVAL2+1^ROSETTA +3 TRUE
Nanoquery
Nanoquery does not short-circuit by default, so short-circuit logic functions have been implemented by nested ifs. <lang nanoquery>def short_and(bool1, bool2)
global a global b if a(bool1) if b(bool2) return true else return false end else return false end
end
def short_or(bool1, bool2)
if a(bool1) return true else if b(bool2) return true else return false end end
end
def a(bool)
println "a called." return bool
end
def b(bool)
println "b called." return bool
end
println "F and F = " + short_and(false, false) + "\n" println "F or F = " + short_or(false, false) + "\n"
println "F and T = " + short_and(false, true) + "\n" println "F or T = " + short_or(false, true) + "\n"
println "T and F = " + short_and(true, false) + "\n" println "T or F = " + short_or(true, false) + "\n"
println "T and T = " + short_and(true, true) + "\n" println "T or T = " + short_or(true, true) + "\n"</lang>

Output:
a called. F and F = false a called. b called. F or F = false a called. F and T = false a called. b called. F or T = true a called. b called. T and F = false a called. T or F = true a called. b called. T and T = true a called. T or T = true
Nemerle
<lang Nemerle>using System.Console;
class ShortCircuit {
public static a(x : bool) : bool { WriteLine("a"); x }
public static b(x : bool) : bool { WriteLine("b"); x } public static Main() : void { def t = true; def f = false;
WriteLine("True && True : {0}", a(t) && b(t)); WriteLine("True && False: {0}", a(t) && b(f)); WriteLine("False && True : {0}", a(f) && b(t)); WriteLine("False && False: {0}", a(f) && b(f)); WriteLine("True || True : {0}", a(t) || b(t)); WriteLine("True || False: {0}", a(t) || b(f)); WriteLine("False || True : {0}", a(f) || b(t)); WriteLine("False || False: {0}", a(f) || b(f)); }
}</lang>

Output:
<lang>a b True && True : True a b True && False: False a False && True : False a False && False: False a True || True : True a True || False: True a b False || True : True a b False || False: False</lang>
NetRexx
Translation of: ooRexx
Like OoRexx, NetRexx allows a list of expressions in the condition part of If and When. Evaluation ends with the first of these expressions resulting in boolean true. <lang NetRexx>/* NetRexx */ options replace format comments java crossref symbols nobinary
Parse Version v Say 'Version='v
If a() | b() Then Say 'a and b are true' If \a() | b() Then Say 'Surprise' Else Say 'ok'
If a(), b() Then Say 'a is true' If \a(), b() Then Say 'Surprise' Else Say 'ok: \\a() is false'
Select
When \a(), b() Then Say 'Surprise' Otherwise Say 'ok: \\a() is false (Select)' End
Return
method a private static binary returns boolean
state = Boolean.TRUE.booleanValue() Say '--a returns' state Return state
method b private static binary returns boolean
state = Boolean.TRUE.booleanValue() Say '--b returns' state Return state
</lang>

Output:
Version=NetRexx 3.03 11 Jun 2014 --a returns 1 --b returns 1 a and b are true --a returns 1 --b returns 1 Surprise --a returns 1 a is true --a returns 1 --b returns 1 Surprise --a returns 1 --b returns 1 Surprise
Nim
Nim produces code which uses short-circuit evaluation. <lang nim>proc a(x): bool =
echo "a called" result = x
proc b(x): bool =
echo "b called" result = x
let x = a(false) and b(true) # echoes "a called" let y = a(true) or b(true) # echoes "a called"</lang>
Objeck
In Objeck the Boolean operators & and | short circuit. <lang objeck>class ShortCircuit {
function : a(a : Bool) ~ Bool { "a"->PrintLine(); return a; }
function : b(b : Bool) ~ Bool { "b"->PrintLine(); return b; }
function : Main(args : String[]) ~ Nil { result := a(false) & b(false); "F and F = {$result}"->PrintLine(); result := a(false) | b(false); "F or F = {$result}"->PrintLine();
result := a(false) & b(true); "F and T = {$result}"->PrintLine(); result := a(false) | b(true); "F or T = {$result}"->PrintLine();
result := a(true) & b(false); "T and F = {$result}"->PrintLine(); result := a(true) | b(false); "T or F = {$result}"->PrintLine();
result := a(true) & b(true); "T and T = {$result}"->PrintLine(); result := a(true) | b(true); "T or T = {$result}"->PrintLine(); }
}</lang>
OCaml
<lang ocaml>let a r = print_endline " > function a called"; r let b r = print_endline " > function b called"; r
let test_and b1 b2 =
Printf.printf "# testing (%b && %b)\n" b1 b2; ignore (a b1 && b b2)
let test_or b1 b2 =
Printf.printf "# testing (%b || %b)\n" b1 b2; ignore (a b1 || b b2)
let test_this test =
test true true; test true false; test false true; test false false;

let () =
print_endline "==== Testing and ===="; test_this test_and; print_endline "==== Testing or ===="; test_this test_or;
</lang>

Output:
==== Testing and ==== # testing (true && true) > function a called > function b called # testing (true && false) > function a called > function b called # testing (false && true) > function a called # testing (false && false) > function a called ==== Testing or ==== # testing (true || true) > function a called # testing (true || false) > function a called # testing (false || true) > function a called > function b called # testing (false || false) > function a called > function b called
Ol
<lang scheme> (define (a x)
(print " (a) => " x) x)
(define (b x)
(print " (b) => " x) x)
and
(print " -- and -- ") (for-each (lambda (x y)
(print "let's evaluate '(a as " x ") and (b as " y ")':") (let ((out (and (a x) (b y)))) (print " result is " out))) '(#t #t #f #f) '(#t #f #t #f))
or
(print " -- or -- ") (for-each (lambda (x y)
(print "let's evaluate '(a as " x ") or (b as " y ")':") (let ((out (or (a x) (b y)))) (print " result is " out))) '(#t #t #f #f) '(#t #f #t #f))
</lang>

Output:
-- and -- let's evaluate '(a as #true) and (b as #true)': (a) => #true (b) => #true result is #true let's evaluate '(a as #true) and (b as #false)': (a) => #true (b) => #false result is #false let's evaluate '(a as #false) and (b as #true)': (a) => #false result is #false let's evaluate '(a as #false) and (b as #false)': (a) => #false result is #false -- or -- let's evaluate '(a as #true) or (b as #true)': (a) => #true result is #true let's evaluate '(a as #true) or (b as #false)': (a) => #true result is #true let's evaluate '(a as #false) or (b as #true)': (a) => #false (b) => #true result is #true let's evaluate '(a as #false) or (b as #false)': (a) => #false (b) => #false result is #false
ooRexx
ooRexx allows a list of expressions in the condition part of If and When. Evaluation ends with the first of these expressions resulting in .false (or 0). <lang oorexx>Parse Version v Say 'Version='v If a() | b() Then Say 'a and b are true' If \a() | b() Then Say 'Surprise'
Else Say 'ok'
If a(), b() Then Say 'a is true' If \a(), b() Then Say 'Surprise'
Else Say 'ok: \a() is false'
Select
When \a(), b() Then Say 'Surprise' Otherwise Say 'ok: \a() is false (Select)' End
Exit a: Say 'a returns .true'; Return .true b: Say 'b returns 1'; Return 1 </lang>

Output:
Version=REXX-ooRexx_4.2.0(MT)_32-bit 6.04 22 Feb 2014 a returns .true b returns 1 a and b are true a returns .true b returns 1 Surprise a returns .true b returns 1 a is true a returns .true ok: \a() is false a returns .true ok: \a() is false (Select)
Oz
Oz' andthen and orelse operators are short-circuiting, as indicated by their name. The library functions Bool.and and Bool.or are not short-circuiting, on the other hand. <lang oz>declare
fun {A Answer} AnswerS = {Value.toVirtualString Answer 1 1} in {System.showInfo " % Called function {A "#AnswerS#"} -> "#AnswerS} Answer end
fun {B Answer} AnswerS = {Value.toVirtualString Answer 1 1} in {System.showInfo " % Called function {B "#AnswerS#"} -> "#AnswerS} Answer end
in
for I in [false true] do for J in [false true] do X Y in {System.showInfo "\nCalculating: X = {A I} andthen {B J}"} X = {A I} andthen {B J} {System.showInfo "Calculating: Y = {A I} orelse {B J}"} Y = {A I} orelse {B J} end end</lang>

Output:
<lang oz>Calculating: X = {A I} andthen {B J}
% Called function {A false} -> false
Calculating: Y = {A I} orelse {B J}
% Called function {A false} -> false % Called function {B false} -> false
Calculating: X = {A I} andthen {B J}
% Called function {A false} -> false
Calculating: Y = {A I} orelse {B J}
% Called function {A false} -> false % Called function {B true} -> true
Calculating: X = {A I} andthen {B J}
% Called function {A true} -> true % Called function {B false} -> false
Calculating: Y = {A I} orelse {B J}
% Called function {A true} -> true
Calculating: X = {A I} andthen {B J}
% Called function {A true} -> true % Called function {B true} -> true
Calculating: Y = {A I} orelse {B J}
% Called function {A true} -> true</lang>
PARI/GP
Note that | and & are deprecated versions of the GP short-circuit operators. <lang parigp>a(n)={
print(a"("n")"); a
}; b(n)={
print("b("n")"); n
}; or(A,B)={
a(A) || b(B)
}; and(A,B)={
a(A) && b(B)
};</lang>
Pascal
Standard Pascal
Standard Pascal doesn't have native short-circuit evaluation. <lang pascal>program shortcircuit(output);
function a(value: boolean): boolean;
begin writeln('a(', value, ')'); a := value end;
function b(value:boolean): boolean;
begin writeln('b(', value, ')'); b := value end;
procedure scandor(value1, value2: boolean);
var result: boolean; begin {and} if a(value1) then result := b(value2) else result := false; writeln(value1, ' and ', value2, ' = ', result);
{or} if a(value1) then result := true else result := b(value2) writeln(value1, ' or ', value2, ' = ', result); end;
begin
scandor(false, false); scandor(false, true); scandor(true, false); scandor(true, true);
end.</lang>
Turbo Pascal
Turbo Pascal allows short circuit evaluation with a compiler switch: <lang pascal>program shortcircuit;
function a(value: boolean): boolean;
begin writeln('a(', value, ')'); a := value; end;
function b(value:boolean): boolean;
begin writeln('b(', value, ')'); b := value; end;
{$B-} {enable short circuit evaluation} procedure scandor(value1, value2: boolean);
var result: boolean; begin result := a(value1) and b(value); writeln(value1, ' and ', value2, ' = ', result);
result := a(value1) or b(value2); writeln(value1, ' or ', value2, ' = ', result); end;
begin
scandor(false, false); scandor(false, true); scandor(true, false); scandor(true, true);
end.</lang>
Extended Pascal
The extended Pascal standard introduces the operators and_then and or_else for short-circuit evaluation. <lang pascal>program shortcircuit(output);
function a(value: boolean): boolean;
begin writeln('a(', value, ')'); a := value end;
function b(value:boolean): boolean;
begin writeln('b(', value, ')'); b := value end;
procedure scandor(value1, value2: boolean);
var result: integer; begin result := a(value1) and_then b(value) writeln(value1, ' and ', value2, ' = ', result);
result := a(value1) or_else b(value2); writeln(value1, ' or ', value2, ' = ', result) end;
begin
scandor(false, false); scandor(false, true); scandor(true, false); scandor(true, true);
end.</lang> Note: GNU Pascal allows and then and or else as alternatives to and_then and or_else.
Perl
Perl uses short-circuit boolean evaluation. <lang Perl>sub a { print 'A'; return $_[0] } sub b { print 'B'; return $_[0] }
Test-driver
sub test {
for my $op ('&&','||') { for (qw(1,1 1,0 0,1 0,0)) { my ($x,$y) = /(.),(.)/; print my $str = "a($x) $op b($y)", ': '; eval $str; print "\n"; } }
}
Test and display
test();</lang>

Output:
a(1) && b(1): AB a(1) && b(0): AB a(0) && b(1): A a(0) && b(0): A a(1) || b(1): A a(1) || b(0): A a(0) || b(1): AB a(0) || b(0): AB
Phix
In Phix all expressions are short circuited<lang Phix>function a(integer i)
printf(1,"a ") return i
end function
function b(integer i)
printf(1,"b ") return i
end function
for z=0 to 1 do
for i=0 to 1 do for j=0 to 1 do if z then printf(1,"a(%d) and b(%d) ",{i,j}) printf(1," => %d\n",a(i) and b(j)) else printf(1,"a(%d) or b(%d) ",{i,j}) printf(1," => %d\n",a(i) or b(j)) end if end for end for
end for</lang>

Output:
a(0) or b(0) a b => 0 a(0) or b(1) a b => 1 a(1) or b(0) a => 1 a(1) or b(1) a => 1 a(0) and b(0) a => 0 a(0) and b(1) a => 0 a(1) and b(0) a b => 0 a(1) and b(1) a b => 1
PicoLisp
<lang PicoLisp>(de a (F)
(msg 'a) F )
(de b (F)
(msg 'b) F )
(mapc
'((I J) (for Op '(and or) (println I Op J '-> (Op (a I) (b J))) ) ) '(NIL NIL T T) '(NIL T NIL T) )</lang>

Output:
a NIL and NIL -> NIL a b NIL or NIL -> NIL a NIL and T -> NIL a b NIL or T -> T a b T and NIL -> NIL a T or NIL -> T a b T and T -> T a T or T -> T
Pike
<lang Pike>int(0..1) a(int(0..1) i) {
write(" a\n"); return i;
}
int(0..1) b(int(0..1) i) {
write(" b\n"); return i;
}
foreach(({ ({ false, false }), ({ false, true }), ({ true, true }), ({ true, false }) });; array(int) args) {
write(" %d && %d\n", @args); a(args[0]) && b(args[1]); write(" %d || %d\n", @args); a(args[0]) || b(args[1]);
}</lang>

Output:
0 && 0 a 0 || 0 a b 0 && 1 a 0 || 1 a b 1 && 1 a b 1 || 1 a 1 && 0 a b 1 || 0 a
PL/I
<lang pli>short_circuit_evaluation:
procedure options (main); declare (true initial ('1'b), false initial ('0'b) ) bit (1); declare (i, j, x, y) bit (1);
a: procedure (bv) returns (bit(1));
declare bv bit(1); put ('Procedure ' || procedurename() || ' called.'); return (bv);
end a; b: procedure (bv) returns (bit(1));
declare bv bit(1); put ('Procedure ' || procedurename() || ' called.'); return (bv);
end b;
do i = true, false; do j = true, false; put skip(2) list ('Evaluating x with <a> with ' || i || ' and with ' || j); put skip; if a(i) then x = b(j); else x = false; put skip data (x); put skip(2) list ('Evaluating y with <a> with ' || i || ' and with ' || j); put skip; if a(i) then y = true; else y = b(j); put skip data (y); end; end;
end short_circuit_evaluation;</lang>

Results:
Evaluating x with <a> with 1 and with 1 Procedure A called. Procedure B called. X='1'B; Evaluating y with <a> with 1 and with 1 Procedure A called. Y='1'B; Evaluating x with <a> with 1 and with 0 Procedure A called. Procedure B called. X='0'B; Evaluating y with <a> with 1 and with 0 Procedure A called. Y='1'B; Evaluating x with <a> with 0 and with 1 Procedure A called. X='0'B; Evaluating y with <a> with 0 and with 1 Procedure A called. Procedure B called. Y='1'B; Evaluating x with <a> with 0 and with 0 Procedure A called. X='0'B; Evaluating y with <a> with 0 and with 0 Procedure A called. Procedure B called. Y='0'B;
PowerShell
PowerShell handles this natively. <lang powershell># Simulated fast function function a ( [boolean]$J ) { return $J }
Simulated slow function
function b ( [boolean]$J ) { Sleep -Seconds 2; return $J }
These all short-circuit and do not evaluate the right hand function
( a $True ) -or ( b $False ) ( a $True ) -or ( b $True ) ( a $False ) -and ( b $False ) ( a $False ) -and ( b $True )
Measure of execution time
Measure-Command { ( a $True ) -or ( b $False ) ( a $True ) -or ( b $True ) ( a $False ) -and ( b $False ) ( a $False ) -and ( b $True ) } | Select TotalMilliseconds
These all appropriately do evaluate the right hand function
( a $False ) -or ( b $False ) ( a $False ) -or ( b $True ) ( a $True ) -and ( b $False ) ( a $True ) -and ( b $True )
Measure of execution time
Measure-Command { ( a $False ) -or ( b $False ) ( a $False ) -or ( b $True ) ( a $True ) -and ( b $False ) ( a $True ) -and ( b $True ) } | Select TotalMilliseconds</lang>

Output:
True True False False TotalMilliseconds ----------------- 15.653 False True False True 8012.9405
Prolog
Prolog has not functions but predicats succeed of fail. Tested with SWI-Prolog. Should work with other dialects. <lang Prolog>short_circuit :- ( a_or_b(true, true) -> writeln('==> true'); writeln('==> false')) , nl, ( a_or_b(true, false)-> writeln('==> true'); writeln('==> false')) , nl, ( a_or_b(false, true)-> writeln('==> true'); writeln('==> false')) , nl, ( a_or_b(false, false)-> writeln('==> true'); writeln('==> false')) , nl, ( a_and_b(true, true)-> writeln('==> true'); writeln('==> false')) , nl, ( a_and_b(true, false)-> writeln('==> true'); writeln('==> false')) , nl, ( a_and_b(false, true)-> writeln('==> true'); writeln('==> false')) , nl, ( a_and_b(false, false)-> writeln('==> true'); writeln('==> false')) .

a_and_b(X, Y) :- format('a(~w) and b(~w)~n', [X, Y]), ( a(X), b(Y)).
a_or_b(X, Y) :- format('a(~w) or b(~w)~n', [X, Y]), ( a(X); b(Y)).
a(X) :- format('a(~w)~n', [X]), X.
b(X) :- format('b(~w)~n', [X]), X.</lang>

Output:
<lang Prolog>?- short_circuit. a(true) or b(true) a(true) ==> true
a(true) or b(false) a(true) ==> true
a(false) or b(true) a(false) b(true) ==> true
a(false) or b(false) a(false) b(false) ==> false
a(true) and b(true) a(true) b(true) ==> true
a(true) and b(false) a(true) b(false) ==> false
a(false) and b(true) a(false) ==> false
a(false) and b(false) a(false) ==> false
true.</lang>
PureBasic
Logical And & Or operators will not evaluate their right-hand expression if the outcome can be determined from the value of the left-hand expression. <lang PureBasic>Procedure a(arg)
PrintN(" # Called function a("+Str(arg)+")") ProcedureReturn arg
EndProcedure
Procedure b(arg)
PrintN(" # Called function b("+Str(arg)+")") ProcedureReturn arg
EndProcedure
OpenConsole() For a=#False To #True
For b=#False To #True PrintN(#CRLF$+"Calculating: x = a("+Str(a)+") And b("+Str(b)+")") x= a(a) And b(b) PrintN("Calculating: x = a("+Str(a)+") Or b("+Str(b)+")") y= a(a) Or b(b) Next
Next Input()</lang>

Output:
Calculating: x = a(0) And b(0) # Called function a(0) Calculating: x = a(0) Or b(0) # Called function a(0) # Called function b(0) Calculating: x = a(0) And b(1) # Called function a(0) Calculating: x = a(0) Or b(1) # Called function a(0) # Called function b(1) Calculating: x = a(1) And b(0) # Called function a(1) # Called function b(0) Calculating: x = a(1) Or b(0) # Called function a(1) Calculating: x = a(1) And b(1) # Called function a(1) # Called function b(1) Calculating: x = a(1) Or b(1) # Called function a(1)
Python
Pythons and and or binary, infix, boolean operators will not evaluate their right-hand expression if the outcome can be determined from the value of the left-hand expression. <lang python>>>> def a(answer): print(" # Called function a(%r) -> %r" % (answer, answer)) return answer
>>> def b(answer): print(" # Called function b(%r) -> %r" % (answer, answer)) return answer
>>> for i in (False, True): for j in (False, True): print ("\nCalculating: x = a(i) and b(j)") x = a(i) and b(j) print ("Calculating: y = a(i) or b(j)") y = a(i) or b(j)

Calculating: x = a(i) and b(j)
# Called function a(False) -> False
Calculating: y = a(i) or b(j)
# Called function a(False) -> False # Called function b(False) -> False
Calculating: x = a(i) and b(j)
# Called function a(False) -> False
Calculating: y = a(i) or b(j)
# Called function a(False) -> False # Called function b(True) -> True
Calculating: x = a(i) and b(j)
# Called function a(True) -> True # Called function b(False) -> False
Calculating: y = a(i) or b(j)
# Called function a(True) -> True
Calculating: x = a(i) and b(j)
# Called function a(True) -> True # Called function b(True) -> True
Calculating: y = a(i) or b(j)
# Called function a(True) -> True</lang>
Pythons if expression can also be used to the same ends (but probably should not): <lang python>>>> for i in (False, True): for j in (False, True): print ("\nCalculating: x = a(i) and b(j) using x = b(j) if a(i) else False") x = b(j) if a(i) else False print ("Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True") y = b(j) if not a(i) else True

Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(False) -> False
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(False) -> False # Called function b(False) -> False
Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(False) -> False
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(False) -> False # Called function b(True) -> True
Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(True) -> True # Called function b(False) -> False
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(True) -> True
Calculating: x = a(i) and b(j) using x = b(j) if a(i) else False
# Called function a(True) -> True # Called function b(True) -> True
Calculating: y = a(i) or b(j) using y = b(j) if not a(i) else True
# Called function a(True) -> True</lang>
R
The builtins && and || will short circuit:
Translation of: Perl
<lang r>a <- function(x) {cat("a called\n"); x} b <- function(x) {cat("b called\n"); x}
tests <- expand.grid(op=list(quote(`||`), quote(`&&`)), x=c(1,0), y=c(1,0))
invisible(apply(tests, 1, function(row) {
call <- substitute(op(a(x),b(y)), row) cat(deparse(call), "->", eval(call), "\n\n")
}))</lang>

Output:
<lang r>a called a(1) || b(1) -> TRUE
a called b called a(1) && b(1) -> TRUE
a called b called a(0) || b(1) -> TRUE
a called a(0) && b(1) -> FALSE
a called a(1) || b(0) -> TRUE
a called b called a(1) && b(0) -> FALSE
a called b called a(0) || b(0) -> FALSE
a called a(0) && b(0) -> FALSE </lang> Because R waits until function arguments are needed before evaluating them, user-defined functions can also short circuit. <lang r>switchop <- function(s, x, y) {
if(s < 0) x || y else if (s > 0) x && y else xor(x, y)
}</lang>

Output:
<lang r>> switchop(-1, a(1), b(1)) a called [1] TRUE > switchop(1, a(1), b(1)) a called b called [1] TRUE > switchop(1, a(0), b(1)) a called [1] FALSE > switchop(0, a(0), b(1)) a called b called [1] TRUE</lang>
Racket
<lang racket>#lang racket (define (a x)
(display (~a "a:" x " ")) x)
(define (b x)
(display (~a "b:" x " ")) x)
(for* ([x '(#t #f)]
[y '(#t #f)]) (displayln `(and (a ,x) (b ,y))) (and (a x) (b y)) (newline) (displayln `(or (a ,x) (b ,y))) (or (a x) (b y)) (newline))</lang>

Output:
(and (a #t) (b #t)) a:#t b:#t (or (a #t) (b #t)) a:#t (and (a #t) (b #f)) a:#t b:#f (or (a #t) (b #f)) a:#t (and (a #f) (b #t)) a:#f (or (a #f) (b #t)) a:#f b:#t (and (a #f) (b #f)) a:#f (or (a #f) (b #f)) a:#f b:#f
Raku
(formerly Perl 6)
Works with: rakudo version 2018.03
<lang perl6>use MONKEY-SEE-NO-EVAL;
sub a ($p) { print 'a'; $p } sub b ($p) { print 'b'; $p }
for 1, 0 X 1, 0 -> ($p, $q) {
for '&&', '||' -> $op { my $s = "a($p) $op b($q)"; print "$s: "; EVAL $s; print "\n"; }
}</lang>

Output:
a(1) && b(1): ab a(1) || b(1): a a(1) && b(0): ab a(1) || b(0): a a(0) && b(1): a a(0) || b(1): ab a(0) && b(0): a a(0) || b(0): ab
REXX
The REXX language doesn't have native short circuits (it's specifically mentioned in the language specifications that
short-circuiting is not supported). <lang rexx>/*REXX programs demonstrates short─circuit evaluation testing (in an IF statement).*/ parse arg LO HI . /*obtain optional arguments from the CL*/ if LO== | LO=="," then LO= -2 /*Not specified? Then use the default.*/ if HI== | HI=="," then HI= 2 /* " " " " " " */
do j=LO to HI /*process from the low to the high.*/ x=a(j) & b(j) /*compute function A and function B */ y=a(j) | b(j) /* " " " or " " */ if \y then y=b(j) /* " " B (for negation).*/ say copies('═', 30) ' x=' || x ' y='y ' j='j say end /*j*/
exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ a: say ' A entered with:' arg(1); return abs( arg(1) // 2) /*1=odd, 0=even */ b: say ' B entered with:' arg(1); return arg(1) < 0 /*1=neg, 0=if not*/</lang>

output when using the default inputs:
B entered with: -2 A entered with: -2 B entered with: -2 A entered with: -2 ══════════════════════════════ x=0 y=1 j=-2 B entered with: -1 A entered with: -1 B entered with: -1 A entered with: -1 ══════════════════════════════ x=1 y=1 j=-1 B entered with: 0 A entered with: 0 B entered with: 0 A entered with: 0 B entered with: 0 ══════════════════════════════ x=0 y=0 j=0 B entered with: 1 A entered with: 1 B entered with: 1 A entered with: 1 ══════════════════════════════ x=0 y=1 j=1 B entered with: 2 A entered with: 2 B entered with: 2 A entered with: 2 B entered with: 2 ══════════════════════════════ x=0 y=0 j=2
Ring
<lang ring>
Project : Short-circuit evaluation
for k = 1 to 2
word = ["AND","OR"] see "========= " + word[k] + " ==============" + nl for i = 0 to 1 for j = 0 to 1 see "a(" + i + ") " + word[k] +" b(" + j + ")" + nl res =a(i) if word[k] = "AND" and res != 0 res = b(j) ok if word[k] = "OR" and res = 0 res = b(j) ok next next
next
func a(t)
see char(9) + "calls func a" + nl a = t return a
func b(t)
see char(9) + "calls func b" + nl b = t return b
</lang> Output:
========= AND ============== a(0) AND b(0) calls func a a(0) AND b(1) calls func a a(1) AND b(0) calls func a calls func b a(1) AND b(1) calls func a calls func b ========= OR ============== a(0) OR b(0) calls func a calls func b a(0) OR b(1) calls func a calls func b a(1) OR b(0) calls func a a(1) OR b(1) calls func a
Ruby
Binary operators are short-circuiting. Demonstration code: <lang ruby>def a( bool )
puts "a( #{bool} ) called" bool
end
def b( bool )
puts "b( #{bool} ) called" bool
end
[true, false].each do |a_val| [true, false].each do |b_val| puts "a( #{a_val} ) and b( #{b_val} ) is #{a( a_val ) and b( b_val )}." puts puts "a( #{a_val} ) or b( #{b_val} ) is #{a( a_val) or b( b_val )}." puts end end</lang>

Output:
a( true ) called b( true ) called a( true ) and b( true ) is true. a( true ) called a( true ) or b( true ) is true. a( true ) called b( false ) called a( true ) and b( false ) is false. a( true ) called a( true ) or b( false ) is true. a( false ) called a( false ) and b( true ) is false. a( false ) called b( true ) called a( false ) or b( true ) is true. a( false ) called a( false ) and b( false ) is false. a( false ) called b( false ) called a( false ) or b( false ) is false.
Run BASIC
<lang runbasic>for k = 1 to 2 ao$ = word$("AND,OR",k,",") print "========= ";ao$;" ==============" for i = 0 to 1
for j = 0 to 1 print "a("; i; ") ";ao$;" b("; j; ")" res =a(i) 'call always
'print res;"<====" if ao$ = "AND" and res <> 0 then res = b(j) if ao$ = "OR" and res = 0 then res = b(j)
next
next next k end
function a( t)
print chr$(9);"calls func a" a = t
end function
function b( t)
print chr$(9);"calls func b" b = t
end function</lang>
========= AND ============== a(0) AND b(0) calls func a a(0) AND b(1) calls func a a(1) AND b(0) calls func a calls func b a(1) AND b(1) calls func a calls func b ========= OR ============== a(0) OR b(0) calls func a calls func b a(0) OR b(1) calls func a calls func b a(1) OR b(0) calls func a a(1) OR b(1) calls func a
Rust
<lang rust>fn a(foo: bool) -> bool {
println!("a"); foo
}
fn b(foo: bool) -> bool {
println!("b"); foo
}
fn main() {
for i in vec![true, false] { for j in vec![true, false] { println!("{} and {} == {}", i, j, a(i) && b(j)); println!("{} or {} == {}", i, j, a(i) || b(j)); println!(); } }
}</lang>

Output:
a b true and true == true a true or true == true a b true and false == false a true or false == true a false and true == false a b false or true == true a false and false == false a b false or false == false
Sather
<lang sather>class MAIN is
a(v:BOOL):BOOL is #OUT + "executing a\n"; return v; end; b(v:BOOL):BOOL is #OUT + "executing b\n"; return v; end; main is x:BOOL;
x := a(false) and b(true); #OUT + "F and T = " + x + "\n\n";
x := a(true) or b(true); #OUT + "T or T = " + x + "\n\n";
x := a(true) and b(false); #OUT + "T and T = " + x + "\n\n";
x := a(false) or b(true); #OUT + "F or T = " + x + "\n\n"; end;
end;</lang>
Scala
<lang scala>object ShortCircuit {
def a(b:Boolean)={print("Called A=%5b".format(b));b} def b(b:Boolean)={print(" -> B=%5b".format(b));b}
def main(args: Array[String]): Unit = { val boolVals=List(false,true) for(aa<-boolVals; bb<-boolVals){ print("\nTesting A=%5b AND B=%5b -> ".format(aa, bb)) a(aa) && b(bb) } for(aa<-boolVals; bb<-boolVals){ print("\nTesting A=%5b OR B=%5b -> ".format(aa, bb)) a(aa) || b(bb) } println }
}</lang>

Output:
Testing A=false AND B=false -> Called A=false Testing A=false AND B= true -> Called A=false Testing A= true AND B=false -> Called A= true -> B=false Testing A= true AND B= true -> Called A= true -> B= true Testing A=false OR B=false -> Called A=false -> B=false Testing A=false OR B= true -> Called A=false -> B= true Testing A= true OR B=false -> Called A= true Testing A= true OR B= true -> Called A= true
Scheme
<lang scheme>>(define (a x)
(display "a\n") x)
>(define (b x)
(display "b\n") x)
>(for-each (lambda (i)
(for-each (lambda (j) (display i) (display " and ") (display j) (newline) (and (a i) (b j)) (display i) (display " or ") (display j) (newline) (or (a i) (b j)) ) '(#t #f)) ) '(#t #f))
t and #t
a b
t or #t
a
t and #f
a b
t or #f
a
f and #t
a
f or #t
a b
f and #f
a
f or #f
a b </lang>
Seed7
<lang seed7>$ include "seed7_05.s7i";
const func boolean: a (in boolean: aBool) is func
result var boolean: result is FALSE; begin writeln("a"); result := aBool; end func;
const func boolean: b (in boolean: aBool) is func
result var boolean: result is FALSE; begin writeln("b"); result := aBool; end func;
const proc: test (in boolean: param1, in boolean: param2) is func
begin writeln(param1 <& " and " <& param2 <& " = " <& a(param1) and b(param2)); writeln(param1 <& " or " <& param2 <& " = " <& a(param1) or b(param2)); end func;
const proc: main is func
begin test(FALSE, FALSE); test(FALSE, TRUE); test(TRUE, FALSE); test(TRUE, TRUE); end func;</lang>

Output:
a FALSE and FALSE = FALSE a b FALSE or FALSE = FALSE a FALSE and TRUE = FALSE a b FALSE or TRUE = TRUE a b TRUE and FALSE = FALSE a TRUE or FALSE = TRUE a b TRUE and TRUE = TRUE a TRUE or TRUE = TRUE
Sidef
<lang ruby>func a(bool) { print 'A'; return bool } func b(bool) { print 'B'; return bool }
Test-driver
func test() {
for op in ['&&', '||'] { for x,y in [[1,1],[1,0],[0,1],[0,0]] { "a(%s) %s b(%s): ".printf(x, op, y) eval "a(Bool(x)) #{op} b(Bool(y))" print "\n" } }
}
Test and display
test()</lang>

Output:
a(1) && b(1): AB a(1) && b(0): AB a(0) && b(1): A a(0) && b(0): A a(1) || b(1): A a(1) || b(0): A a(0) || b(1): AB a(0) || b(0): AB
Simula
<lang simula>BEGIN
BOOLEAN PROCEDURE A(BOOL); BOOLEAN BOOL; BEGIN OUTCHAR('A'); A := BOOL; END A;
BOOLEAN PROCEDURE B(BOOL); BOOLEAN BOOL; BEGIN OUTCHAR('B'); B := BOOL; END B;
PROCEDURE OUTBOOL(BOOL); BOOLEAN BOOL; OUTCHAR(IF BOOL THEN 'T' ELSE 'F');
PROCEDURE TEST; BEGIN PROCEDURE ANDTEST; BEGIN BOOLEAN X, Y, Z; FOR X := TRUE, FALSE DO FOR Y := TRUE, FALSE DO BEGIN OUTTEXT("A("); OUTBOOL(X); OUTTEXT(") AND "); OUTTEXT("B("); OUTBOOL(Y); OUTTEXT("): "); Z := A(X) AND THEN B(Y); OUTIMAGE; END; END ANDTEST;
PROCEDURE ORTEST; BEGIN BOOLEAN X, Y, Z; FOR X := TRUE, FALSE DO FOR Y := TRUE, FALSE DO BEGIN OUTTEXT("A("); OUTBOOL(X); OUTTEXT(") OR "); OUTTEXT("B("); OUTBOOL(Y); OUTTEXT("): "); Z := A(X) OR ELSE B(Y); OUTIMAGE; END; END ORTEST;
ANDTEST; ORTEST;
END TEST;
TEST;
END. </lang>

Output:
A(T) AND B(T): AB A(T) AND B(F): AB A(F) AND B(T): A A(F) AND B(F): A A(T) OR B(T): A A(T) OR B(F): A A(F) OR B(T): AB A(F) OR B(F): AB
Smalltalk
Works with: GNU Smalltalk
The and: or: selectors are shortcircuit selectors but in order to avoid evaluation of the second operand, it must be a block: a and: [ code ] will evaluate the code only if a is true. On the other hand, a and: b, where b is an expression (not a block), behaves like the non-shortcircuit and (&). (Same speech for or |) <lang smalltalk>Smalltalk at: #a put: nil. Smalltalk at: #b put: nil.
a := [:x| 'executing a' displayNl. x]. b := [:x| 'executing b' displayNl. x].
('false and false = %1' %
{ (a value: false) and: [ b value: false ] }) displayNl.
('true or false = %1' %
{ (a value: true) or: [ b value: false ] }) displayNl.
('false or true = %1' %
{ (a value: false) or: [ b value: true ] }) displayNl.
('true and false = %1' %
{ (a value: true) and: [ b value: false ] }) displayNl.</lang>
SNOBOL4
Because of its unique success/failure model of flow control, Snobol does not use standard boolean operators or assignment. However, in &fullscan mode Snobol exhibits short-circuit boolean behavior in pattern matches, with concatenation " " functioning as logical AND, and alternation " | " as logical OR.
The test statements below use a pattern constructed from the functions a( ) and b( ) and match it to the null string with deferred evaluation. This idiom allows the functions to self-report the expected short-circuit patterns. <lang SNOBOL4> define('a(val)') :(a_end) a out = 'A '
eq(val,1) :s(return)f(freturn)
a_end
define('b(val)') :(b_end)
b out = 'B '
eq(val,1) :s(return)f(freturn)
b_end
# Test and display
&fullscan = 1 output(.out,1,'-[-r1]') ;* Macro Spitbol
output(.out,1,'B','-') ;* CSnobol
define('nl()'):(nlx);nl output = :(return);nlx out = 'T and T: '; null ? *a(1) *b(1); nl() out = 'T and F: '; null ? *a(1) *b(0); nl() out = 'F and T: '; null ? *a(0) *b(1); nl() out = 'F and F: '; null ? *a(0) *b(0); nl() output = out = 'T or T: '; null ? *a(1) | *b(1); nl() out = 'T or F: '; null ? *a(1) | *b(0); nl() out = 'F or T: '; null ? *a(0) | *b(1); nl() out = 'F or F: '; null ? *a(0) | *b(0); nl()
end</lang>

Output:
T and T: A B T and F: A B F and T: A F and F: A T or T: A T or F: A F or T: A B F or F: A B
Standard ML
Translation of: OCaml
<lang sml>fun a r = ( print " > function a called\n"; r ) fun b r = ( print " > function b called\n"; r )
fun test_and b1 b2 = (
print ("# testing (" ^ Bool.toString b1 ^ " andalso " ^ Bool.toString b2 ^ ")\n"); ignore (a b1 andalso b b2) )
fun test_or b1 b2 = (
print ("# testing (" ^ Bool.toString b1 ^ " orelse " ^ Bool.toString b2 ^ ")\n"); ignore (a b1 orelse b b2) )
fun test_this test = (
test true true; test true false; test false true; test false false )

print "==== Testing and ====\n"; test_this test_and; print "==== Testing or ====\n"; test_this test_or;</lang>

Output:
==== Testing and ==== # testing (true andalso true) > function a called > function b called # testing (true andalso false) > function a called > function b called # testing (false andalso true) > function a called # testing (false andalso false) > function a called ==== Testing or ==== # testing (true orelse true) > function a called # testing (true orelse false) > function a called # testing (false orelse true) > function a called > function b called # testing (false orelse false) > function a called > function b called
Stata
Stata always evaluates both arguments of operators & and |. Here is a solution with if statements.
<lang stata>function a(x) { printf(" a") return(x) }
function b(x) { printf(" b") return(x) }
function call(i, j) { printf("and:") x = a(i) if (x) { x = b(j) } printf("\nor:") y = a(i) if (!y) { y = b(j) } printf("\n") return((x,y)) }</lang>
Example
<lang stata>: call(0,1) and: a or: a b
1 2 +---------+ 1 | 0 1 | +---------+
call(1,1)
and: a b or: a
1 2 +---------+ 1 | 1 1 | +---------+</lang>
Swift
Short circuit operators are && and ||. <lang swift>func a(v: Bool) -> Bool {
print("a") return v
}
func b(v: Bool) -> Bool {
print("b") return v
}
func test(i: Bool, j: Bool) {
println("Testing a(\(i)) && b(\(j))") print("Trace: ") println("\nResult: \(a(i) && b(j))") println("Testing a(\(i)) || b(\(j))") print("Trace: ") println("\nResult: \(a(i) || b(j))") println()
}
test(false, false) test(false, true) test(true, false) test(true, true)</lang>

Output:
Testing a(false) && b(false) Trace: a Result: false Testing a(false) || b(false) Trace: ab Result: false Testing a(false) && b(true) Trace: a Result: false Testing a(false) || b(true) Trace: ab Result: true Testing a(true) && b(false) Trace: ab Result: false Testing a(true) || b(false) Trace: a Result: true Testing a(true) && b(true) Trace: ab Result: true Testing a(true) || b(true) Trace: a Result: true
Tcl
The && and || in the expr command support short-circuit evaluation. It is recommended that you always put expressions in braces so that and command or variable substitutions are applied at the right time rather than before the expression is evaluated at all. (Indeed, it is recommended that you do that anyway as unbraced expressions cannot be efficiently compiled.) <lang tcl>package require Tcl 8.5 proc tcl::mathfunc::a boolean {
puts "a($boolean) called" return $boolean
} proc tcl::mathfunc::b boolean {
puts "b($boolean) called" return $boolean
}
foreach i {false true} {
foreach j {false true} { set x [expr {a($i) && b($j)}] puts "x = a($i) && b($j) = $x" set y [expr {a($i) || b($j)}] puts "y = a($i) || b($j) = $y" puts ""; # Blank line for clarity }
}</lang>

Output:

Note that booleans may be written out words or numeric

a(false) called x = a(false) && b(false) = 0 a(false) called b(false) called y = a(false) || b(false) = 0 a(false) called x = a(false) && b(true) = 0 a(false) called b(true) called y = a(false) || b(true) = 1 a(true) called b(false) called x = a(true) && b(false) = 0 a(true) called y = a(true) || b(false) = 1 a(true) called b(true) called x = a(true) && b(true) = 1 a(true) called y = a(true) || b(true) = 1
TXR
<lang txr>@(define a (x out)) @ (output)
a (@x) called
@ (end) @ (bind out x) @(end) @(define b (x out)) @ (output)
b (@x) called
@ (end) @ (bind out x) @(end) @(define short_circuit_demo (i j)) @ (output) a(@i) and b(@j): @ (end) @ (maybe) @ (a i "1") @ (b j "1") @ (end) @ (output) a(@i) or b(@j): @ (end) @ (cases) @ (a i "1") @ (or) @ (b j "1") @ (or) @ (accept) @ (end) @(end) @(short_circuit_demo "0" "0") @(short_circuit_demo "0" "1") @(short_circuit_demo "1" "0") @(short_circuit_demo "1" "1")</lang>

Run:
$ txr short-circuit-bool.txr a(0) and b(0): a (0) called a(0) or b(0): a (0) called b (0) called a(0) and b(1): a (0) called a(0) or b(1): a (0) called b (1) called a(1) and b(0): a (1) called b (0) called a(1) or b(0): a (1) called a(1) and b(1): a (1) called b (1) called a(1) or b(1): a (1) called
The a and b functions are defined such that the second parameter is intended to be an unbound variable. When the function binds out, that value propagates back to the unbound variable at the call site. But the way calls works in this language allows us to specify a value instead such as "1". So now the directive @(bind out x) performs unification instead: if x doesn't match "1", the function fails, otherwise it succeeds.
So simply by placing two calls consecutively, we get a short circuting conjunction. The second will not execute if the first one fails.
Short-circuiting disjunction is provided by @(cases).
The @(maybe) construct stops failure from propagating from the enclosed subquery. The @(accept) directive will bail out of the closest enclosing anonymous block (the function body) with a success. It prevents the @(cases) from failing the function if neither case is successful.
UNIX Shell
The && and || operators use the exit status of each command. The true and false commands convert a string to an exit status; our code && x=true || x=false converts an exit status to a string.
Works with: Bourne Shell
<lang bash>a() { echo "Called a $1" "$1" }
b() { echo "Called b $1" "$1" }
for i in false true; do for j in false true; do a $i && b $j && x=true || x=false echo " $i && $j is $x"
a $i || b $j && y=true || y=false echo " $i || $j is $y" done done</lang> The output reveals that && and || have short-circuit evaluation.
Called a false false && false is false Called a false Called b false false || false is false Called a false false && true is false Called a false Called b true false || true is true Called a true Called b false true && false is false Called a true true || false is true Called a true Called b true true && true is true Called a true true || true is true
C Shell
Between commands, && and || have short-circuit evaluation. (The aliases for a and b must expand to a single command; these aliases expand to an eval command.) <lang csh>alias a eval \echo "Called a \!:1"; "\!:1"'\' alias b eval \echo "Called b \!:1"; "\!:1"'\'
foreach i (false true) foreach j (false true) a $i && b $j && set x=true || set x=false echo " $i && $j is $x"
a $i || b $j && set x=true || set x=false echo " $i || $j is $x" end end</lang> Inside expressions, && and || can short circuit some commands, but cannot prevent substitutions. <lang csh># Succeeds, only prints "ok". if ( 1 || { echo This command never runs. } ) echo ok
Fails, aborts shell with "bad: Undefined variable".
if ( 1 || $bad ) echo ok
Prints "error", then "ok".
if ( 1 || `echo error >/dev/stderr` ) echo ok</lang>
VBA
<lang vb>Private Function a(i As Variant) As Boolean
Debug.Print "a: "; i = 1, a = i
End Function Private Function b(j As Variant) As Boolean
Debug.Print "b: "; j = 1; b = j
End Function Public Sub short_circuit()
Dim x As Boolean, y As Boolean 'Dim p As Boolean, q As Boolean Debug.Print "=====AND=====" & vbCrLf For p = 0 To 1 For q = 0 To 1 If a(p) Then x = b(q) End If Debug.Print " = x" Next q Debug.Print Next p Debug.Print "======OR=====" & vbCrLf For p = 0 To 1 For q = 0 To 1 If Not a(p) Then x = b(q) End If Debug.Print " = x" Next q Debug.Print Next p Debug.Print
End Sub

</lang>

Output:
=====AND=====
a: Onwaar = x a: Onwaar = x
a: Waar b: Onwaar = x a: Waar b: Waar = x
======OR=====
a: Onwaar b: Onwaar = x a: Onwaar b: Waar = x
a: Waar = x
a: Waar = x
Visual Basic .NET
Translation of: c++
<lang vbnet>Module Module1
Function A(v As Boolean) As Boolean Console.WriteLine("a") Return v End Function
Function B(v As Boolean) As Boolean Console.WriteLine("b") Return v End Function
Sub Test(i As Boolean, j As Boolean) Console.WriteLine("{0} and {1} = {2} (eager evaluation)", i, j, A(i) And B(j)) Console.WriteLine("{0} or {1} = {2} (eager evaluation)", i, j, A(i) Or B(j)) Console.WriteLine("{0} and {1} = {2} (lazy evaluation)", i, j, A(i) AndAlso B(j)) Console.WriteLine("{0} or {1} = {2} (lazy evaluation)", i, j, A(i) OrElse B(j))
Console.WriteLine() End Sub
Sub Main() Test(False, False) Test(False, True) Test(True, False) Test(True, True) End Sub
End Module</lang>

Output:
a b False and False = False (eager evaluation) a b False or False = False (eager evaluation) a False and False = False (lazy evaluation) a b False or False = False (lazy evaluation) a b False and True = False (eager evaluation) a b False or True = True (eager evaluation) a False and True = False (lazy evaluation) a b False or True = True (lazy evaluation) a b True and False = False (eager evaluation) a b True or False = True (eager evaluation) a b True and False = False (lazy evaluation) a True or False = True (lazy evaluation) a b True and True = True (eager evaluation) a b True or True = True (eager evaluation) a b True and True = True (lazy evaluation) a True or True = True (lazy evaluation)
Visual FoxPro
<lang vfp>
!* Visual FoxPro natively supports short circuit evaluation
CLEAR CREATE CURSOR funceval(arg1 L, arg2 L, operation V(3), result L, calls V(10))
!* Conjunction
INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .F., "AND") REPLACE result WITH (a(arg1) AND b(arg2)) INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .T., "AND") REPLACE result WITH (a(arg1) AND b(arg2)) INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .F., "AND") REPLACE result WITH (a(arg1) AND b(arg2)) INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .T., "AND") REPLACE result WITH (a(arg1) AND b(arg2))
!* Disjunction
INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .F., "OR") REPLACE result WITH (a(arg1) OR b(arg2)) INSERT INTO funceval (arg1, arg2, operation) VALUES (.F., .T., "OR") REPLACE result WITH (a(arg1) OR b(arg2)) INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .F., "OR") REPLACE result WITH (a(arg1) OR b(arg2)) INSERT INTO funceval (arg1, arg2, operation) VALUES (.T., .T., "OR") REPLACE result WITH (a(arg1) OR b(arg2)) GO TOP
_VFP.DataToClip("funceval", 8, 3)
FUNCTION a(v As Boolean) As Boolean REPLACE calls WITH "a()" RETURN v ENDFUNC
FUNCTION b(v As Boolean) As Boolean REPLACE calls WITH calls + ", b()" RETURN v ENDFUNC </lang>

Output:
Arg1 Arg2 Operation Result Calls F F AND F a() F T AND F a() T F AND F a(), b() T T AND T a(), b() F F OR F a(), b() F T OR T a(), b() T F OR T a() T T OR T a()
Wren
Wren has the && and || short-circuiting operators found in many C family languages. <lang ecmascript>var a = Fn.new { |bool|
System.print(" a called") return bool
}
var b = Fn.new { |bool|
System.print(" b called") return bool
}
var bools = [ [true, true], [true, false], [false, true], [false, false] ] for (bool in bools) {
System.print("a = %(bool[0]), b = %(bool[1]), op = && :") a.call(bool[0]) && b.call(bool[1]) System.print()
}
for (bool in bools) {
System.print("a = %(bool[0]), b = %(bool[1]), op = || :") a.call(bool[0]) || b.call(bool[1]) System.print()
}</lang>

Output:
a = true, b = true, op = && : a called b called a = true, b = false, op = && : a called b called a = false, b = true, op = && : a called a = false, b = false, op = && : a called a = true, b = true, op = || : a called a = true, b = false, op = || : a called a = false, b = true, op = || : a called b called a = false, b = false, op = || : a called b called
zkl
<lang zkl>fcn a(b){self.fcn.println(b); b} fcn b(b){self.fcn.println(b); b}</lang>

Output:
a(True) or b(True) //-->Fcn(a)True, True a(False) or b(True) //-->Fcn(a)False, Fcn(b)True, True a(False) or b(False) //-->Fcn(a)False, Fcn(b)False, False a(True) and b(True) //-->Fcn(a)True, Fcn(b)True, True a(True) and b(False) //-->Fcn(a)True, Fcn(b)False, False a(False) and b(True) //-->Fcn(a)False, False