# Reinvent the For loop [closed]

For loops are used extensively in many languages, but what would you do if no languages supported them?

Create a way to execute a basic for loop without using any repetition structures (for, foreach, while, do, etc).

The basic for loop that you need to replicate is set up like this

for(i=0;i<1000;i++)


You must be able to replicate this without using repetition structures. It must also execute code in your language that would be in the body of the loop. Any form of eval is allowed, though it may not execute the for loop on its own.

You can test your code by having it print i with a space 100 times, add this test case to the end of your answer to verify your code with others.

There are no restrictions on what exactly it has to be, all it needs to do is replicate the for loop.

Winner will be decided based on upvotes at the time that it is chosen.

• 100 times or 1000? Or 100 000 times? Commented Feb 19, 2011 at 6:50
• I find the problem too undefined. You say “without using any repetition structures” and only give examples (but not an extensive list) of such prohibited structures. The answers provided so far use recursion or goto, both of which I would classify as “repetition structures”, but it can be debated. Without a proper definition of what is allowed and what isn’t, this question is not interesting. Commented Mar 8, 2011 at 14:34
• gotos, recursion... Commented Mar 10, 2011 at 2:29
• I am voting to close this as off-topic because we require objective validity criteria for all challenges. As it stands, there is no clear way to determine the validity of a submission. Additionally, there is no specification of the behavior of a valid submission.
– user45941
Commented May 20, 2016 at 5:35

## Windows Batch File, 65

set I=%S%
:l
if %I% GEQ %E% goto :eof
call %C%
set /a I+=1
goto l


Test file:

@echo off
set S=0
set E=100
set "C=<nul set /p X=%%I%% "
call for.cmd


Can save two bytes if the loop always starts at 0.

## Perl (23 chars.):

print join " ",(0..999);*


or same Perl but in simpler yet more lengthy and recursive words:

sub i {($s,$e)=@_; return if $s==$e; print "$s "; i($s+1,$e)} i(0,1000);  ## C#, 70 chars Enumerable.Range(0,999).ToList().ForEach(x=>Console.WriteLine(x+" "));  This can probably be golfed down, but it's the best I could come up with quickly. • Obviously never going to beat Perl, but I didn't see the Perl comment before I posted mine. – B.R. Commented Feb 19, 2011 at 0:07 • The code uses a foreach loop, which isn't allowed in the first post. Commented Feb 19, 2011 at 1:32 • @Bass: no it doesn't. It calls a method that happens to be called ForEach. Commented Feb 19, 2011 at 5:31 • @Martinho, so .each in Ruby and ForEach-Object in PowerShell is fine as well? There are languages that don't even have that many keywords, actually. – Joey Commented Feb 19, 2011 at 17:18 • @Joey: look at how many existing answers use .each, map, range generators, etc. They're just black boxes. Who says they are not using gotos? Commented Feb 19, 2011 at 19:29 ## QuickBASIC, 103 characters 10 IF i < 1000 THEN PRINT MID$(STR$(i) + SPACE$(1), 2, ABS(i < 100) * 5); : i = i + 1: GOTO 10 ELSE END

• Oh dear, after re-reading the requirements it looks like only the numbers 0 through 99 should be printed. Revised entry (and I think I'll have to take a shower after THIS hack): 10 IF i < 1000 THEN PRINT MID$(STR$(i) + SPACE$(1), 2, ABS(i < 100) * 5); : i = i + 1: GOTO 10 ELSE END – user609 Commented Feb 19, 2011 at 1:27 ## Java with Lambda — 259 characters I just built the prerelease Java langtools with the experimental lambda support that has recently been canceled for JDK 7 and pushed back until JDK 8 in 2012 (boo!) and wanted to try it out. Formatted nicely, this version clocks in at 304 characters. If you reformat it so all the code of the interface is on one line and the class is on another, it gets down to 259 characters. I'm sure you could golf it down lower (shorten the identifiers, for starters), but Java is never going to be competitive at golf, so why obfuscate it. interface Fore { void exec(int i); } public class ForLoop { public static void main(String[] args) { loop(1, 10, #{ int i -> System.out.println(i) }); } public static void loop(int x, int max, Fore fore) { fore.exec(x); if (x < max) loop(x+1, max, fore); } }  I just wanted to demonstrate what will be possible with lambdas in Java SE 8. The call to loop could be written with an anonymous inner class, instead: loop(1, 10, new Fore() { public void exec(int i) { System.out.println(i); } });  Yuck. The syntax for lambdas in Java hasn't been settled yet; this is just what works with the current dev build of javac. Thanks to those who are working to make it happen. Java should have gotten lambdas and closures years ago. Alas. ## C (not really golfing, but fun) #include <setjmp.h> #include <stdio.h> int main() { jmp_buf b; int i; if ((i = setjmp(b)) < 100) { printf("%d\n", i); longjmp(b, i + 1); } }  • At least it doesn't use goto. Commented Mar 19, 2011 at 18:29 ## JavaScript, 63 characters (function i(s,r){r+=s+' ';s++<1e3?i(s,r):console.log(r)})(0,'')  with proper console output ## R - 11 characters General case: f(1:1000)  Where f is your function. Specific case: cat(1:1000)  ## C 45 characters including printout Compiles, links, and runs as-is; no need to define a separate function and then call it, adding to source size. main(a){printf("%d ",a-1);a<1000&&main(a+1);}  ## Javascript (44 chars.): Another rather pointless option, but then who said golf had to have a point :) Plus I gained something new... I never realised you could get away with i+++ eval(Array((i=0)+1e3).join('i+++" "+')+'i')  I also learned that running .map and .forEach on an initialised undefined filled Array does nothing... at least in FireFox anyway Array(1000).forEach(function(){ /* this code is never executed :( */ })  • From MDN - callback is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or which have never been assigned values. Commented Nov 20, 2012 at 9:01 • @Gareth yep thanks for the quote, I assumed as much, was just a little unexpected.. and rather annoying from a codegolf point of view :) Commented Nov 20, 2012 at 9:22 # Javascript, 71. No if, for, or recursive function function f(i,c,b){a=[] eval(s=b+";a[++i]=s;a=a.slice(0,c);eval(a[i])")}  Test: f(0,1000,'console.log(i)')  ## Spaghetti PHP 44 <?$i=0;a:if($i<1001){echo$i++." ";goto a;}


# Python 2.7, 60 Bytes with command-line parameter

Prints 'O' to the console:

import sys
def l(t,m):
print 'O'
if t!=m:
l(t+1,m)
l(0,int(sys.argv[0]))


EDIT: Realised it didn't work, so byte count has gone up to fix On another note, here's a 127 byte version, including print function, that will let you actually call functions with one argument

import sys
def println(a):
print(a)
def l(t,m,f,a):
f(a)
if t!=m:
l(t+1,m,f,a)
p=println
l(0,int(sys.argv[1]),p,"there")


# Objective-C 58 Characters (Or 45...)

int i;
-(void)f {
NSLog(@"%d",i++);
if (i<1000) [self f];
}

[self f];


*13 chars went on printing i, so only the for-loop is actually 45...

# sh

cat -An /dev/urandom|head -n1000|cut -f1|xargs

• You can generate infinite lines with "yes". Try "yes ''|head -n1000|cat -n|xargs" Commented Dec 22, 2014 at 19:42

## Python 2.x - 17 chars

print range(1000)

• You need a for loop: print " ".join(i for i in range(1000))
– Wok
Commented Feb 19, 2011 at 9:35
• @wok: the challenge is to not use for-loops. Commented Feb 20, 2011 at 16:26

Language = C

just loop - 59 characters

(int(*)())\x66\x31\xc0\x66\x40\x66\x3d\xe8\x03\x75\xf8\xc3"


loop+call - 92 characters

(int(*)())"\x66\x31\xc0\x8b\x5c\x24\x04\x66\x40\x50\xff\xd3\x58\x66\x3d\xe8\x03\x75\xf4\xc3"


Example usage:

#include <stdio.h>

void disp(int n){printf("%d ", n&(0xffff));}

int main(){
((int(*)())"\x66\x31\xc0\x8b\x5c\x24\x04\x66\x40\x50\xff\xd3\x58\x66\x3d\xe8\x03\x75\xf4\xc3")(&disp);
return 0;
}


This will only work on x86 machines. Tested with gcc (and works on codepad.org -> http://codepad.org/uyhFR9XU)

int fn(int n){ // n is at esp+4

xor %ax, %ax ; zeros ax
mov 4(%esp), %ebx ; saves esp+4 (addr of n) to ebx

body:
inc %ax ; add one to ax (this will print from 1 to 1000 instead of 0-999)
push %eax ; pushes eax onto the stack
call *%ebx ; calls n, which should contain &disp
pop %eax ; pop eax off the stack assuming disp did not use eax
cmp $1000, %ax ; compare jne body ; if not 1000, goto body ret }  • And probably should fail when DEP is enabled. – Joey Commented Feb 19, 2011 at 17:37 • Can you include the char count and language? Commented Feb 19, 2011 at 19:43 • K, information added – Lee Commented Feb 19, 2011 at 21:21 Scala: (1 to 100)mkString" "  21 chars not that ugly: (1 to 100) mkString " "  ### APL (26) {(⊃⍵)>⊃⌽⍵:⍬⋄⍺⍺∇⍵+1 0⊣⍺⍺⊃⍵}  Usage: <function> {(⊃⍵)>⊃⌽⍵:⍬⋄⍺⍺∇⍵+1 0⊣⍺⍺⊃⍵} <start> <end>  i.e. {⍞←⍵ ' '} {(⊃⍵)>⊃⌽⍵:⍬⋄⍺⍺∇⍵+1 0⊣⍺⍺⊃⍵} 1 100  prints the numbers from 1 to 100. VB11 (95c) Dim F As Action(Of Integer, Integer, Action(Of Integer)) = Sub(i, m, a) If i > m Then Return a(i) F(i + 1, i, a) End Sub  And in use  F(1, 1000, Sub(X) Console.WriteLine(X))  C# 52 f(int i,int m, action<int> a){if(i<=m){a(i);f(i-1,m,a);}  # Python 2.6 (42) def f(i,p,j=0):j<i and(p(j)or f(i,p,j+1)) # Test: def do(i): print i f(100,do)  This for-Function also includes the break command: def do(i): print i if i==7: return True # break f(100,do)  ## clang (152) Tested with Apple clang version 4.0 bfor(int n,void(^b)(int)){ __block void(^e)(int,int)=^(int l,int h){ int m; h<l?:(m=(l+h)/2,e(l,m-1),b(m),e(m+1,h)); }; e(0,n-1); }  Usage: main(){ bfor(100,^(int i){ printf("%d ", i); }); puts(""); }  The stack depth is log2 of the count due to the binary tree and thus it's unlikely to overflow due to recursion. ## Ti-84 Basic, 34 Here, > represents the calculator's STO-> button. :-1>I:Lbl A:I+1>I:If I<1000:Goto A  ## Golf-Basic 84, 23 characters :-1_IlA:I++I@I<1000oA  # Lua, 59 local function f(x)if x<1000 then return f(x+1)end end f(0)  The loop body is located right after the then. This does not overflow stack because of the tail call optimization. Test case: local function f(x)if x<1000 then print(x)return f(x+1)end end f(0)  Same as @houbysoft, but in C++. #include <iostream> #include <vector> int main(int argc, char *argv[]) { int i = 0; std::function<int()> m = [&i, &m]()->int { std::vector<std::function<int()>> functors; functors.push_back(m); functors.push_back([]()->int{return 0;}); i++; std::cout << i << std::endl; functors[i>999](); return i; }; m(); return 0; }  And Objective C (Just C using blocks, actually...) #import <Foundation/Foundation.h> int main(int argc, char *argv[]) { __block int i = 0; __block int (^m)(); m = ^() { int (^a[])() = {m, ^(){return 0;}}; i++; NSLog(@"i: %d", i); a[i>9](); return i; }; m(); return 0; }  Nemerle (?c) macro for (init, cond, change, body) syntax ("for", "(", init, ";", cond, ";", change, ")", body) { <[$init;
def loop () : void
{
if ($cond) {$body; \$change; loop() }
else ()
};
loop ()
]>
}


Usage

 for (mutable i = 0, i < 10, i++, printf ("%d", i))


## Lua (63 chars)

function F(n,f,...)if n>0 then f(...)return F(n-1,f,...)end end

Slightly longer, but more generic, than @mniip's version. Use like F(1000,print,' ').

# C - 48 characters

Compilable code.

main(int i){i^1002&&main(i+1);printf("%i",i-2);}


# CPython 2, 158 bytes

(Yes, this is both implementation and version specific)

class K(object):
def __init__(s,b,c,e,n):
if not n:n={};exec b in n
else:exec e in n
s.n=n;s.c=c;s.e=e
def __del__(s):eval(s.c,s.n)or K(0,s.c,s.e,s.n)


Example usage:

K('i=55','i<88','i+=1;print i,0)
`