Loop

Loop is a syntax structure of PapajScript, that allows executing an instruction (or a set of them) multiple times. The first loops were introduced on January 12, 2018, along with the update for RPN Calculator 0.3.0.

First loops

The first ever introduced loop is times-loop, which has 2 syntaxes

Name	Syntax	Purpose	Since	Last supported version
times-loop	Xn I1	Do I1 n times (n >= 1)	0.3.0	0.4.1
times-loop	N1 times I1	Do I1 N1 times	0.3.1	supported today

Currently supported loops

Syntaxes of C-like loops

Name	Syntax	Purpose	Since
times-loop	N1 times I1	Do I1 N1 times	0.3.1
while-loop	while ( B1 ) I1	While B1 is true, do I1	0.5.0
do-while-loop	do I1 while ( B1 )	Repeat doing I1 while B1 is true	0.5.0
do-until-loop	do I1 until ( B1 )	Repeat doing I1 until B1 is true	0.5.0
for-loop	for ( I1 ; B1 ; I2 ) I3	Start a loop with I1 and while B1 is true, do I3 and then I2	0.5.0
for-each-loop	for ( E1 : A1 ) I1	For each element E1 from array A1 do I1	0.5.1
for-each-indexed-loop	for ( J1 E1 : A1 ) I1	For each element E1 with index J1 from array A1 do I1	0.5.2.2

Syntaxes for postfix loops

Name	Syntax	Purpose	Since
callWhile	EXP1 FUN1 function	Checks for a condition expression and repeats the procedure as long as the condition is true (equivalent of C-like while loop)	0.5.2
callWhile	FUN1 EXP1 function	Repeats the procedure as long as the condition contained in the expression is true (equivalent of C-like do-while loop)	0.5.2
callUntil	EXP1 FUN1 function	Checks for a condition expression and repeats the procedure as long as the condition is false	0.5.2
callUntil	FUN1 EXP1 function	Repeats the procedure as long as the condition contained in the expression is false	0.5.2

Notes

• A for-each-loop may overwrite array items' values when assigning
• Prior to the 0.5.3 version, for-each-loop had to contain a pre-defined array, so for ( $i : $T sortNumbers ) { } did not work. A kind of workaround was $T sortNumbers -> $U for ( $i : $U ) { }
• A for-each-loop and for-each-indexed-loop is able to change array's values by default. Since April 17, 2021 (earliest stable version 0.5.2) it is possible to restrict the loop from editing the array by using const word, e.g. for ( const $i : $T ) or for ( const $index $item : $T )

Examples

• 10 times { 100 random } which generates 10 numbers from a range [0..99] (note: we must know the exact amount of iterations here)
• 1 >i while ( i 10 <= ) { 100 random i ++ >i } which also generates 10 numbers from a range [0..99]
• 1 >i do { 100 random i ++ >i } while ( i 10 <= ) which also generates 10 numbers from a range [0..99]
• 1 >i do { 100 random i ++ >i } until ( i 10 > ) which also generates 10 numbers from a range [0..99]
• for ( 1 >i ; i 10 <= ; i ++ >i ) { 100 random } which also generates 10 numbers from a range [0..99]
• for ( item : [ 1 1 10 seq ] ) { i println } prints a sequence from 1 to 10

for ( 1 -> i ; i 5 <= ; i ++ -> i ) { 
    i i * println
} // print squares of numbers 1..5

for ( i : [ 1 1 5 seq ] ) { 
    i i * println
} // print squares of numbers 1..5

[ 1 1 5 seq ] -> $T
$T println // prints [ 1 2 3 4 5 ]
for ( $i : $T ) { 
    $i $i * println
} // print squares of numbers 1..5, i.e. 1, 4, 9, 16, 25
$T println // prints [ 1 4 9 16 25 ]

[ 1 1 5 seq ] -> $T
$T println // prints [ 1 2 3 4 5 ]
for ( const $i : $T ) { 
    $i $i * println
} // print squares of numbers 1..5, i.e. 1, 4, 9, 16, 25
$T println // prints [ 1 2 3 4 5 ]

[ "a" "b" "c" ] -> $T
$T println // prints [ "a" "b" "c" ]
for ( const $i $item : $T ) { 
    $i " - " $item ", " + + + print
} // print `0 - a, 1 - b, 2 - c`
$T println // prints [ "a" "b" "c" ]