[Question]
  [
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---
 Questions without an **objective primary winning criterion** are off-topic, as they make it impossible to indisputably decide which entry should win.
Closed 7 years ago.
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`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.
  
[Answer]
## C, 45 chars without goto, if, for, ...
Not the smallest solution, but I find this way of doing it quite interesting in C :)
Doesn't use `goto`, `if`, `for`, or any other kind of control structures.
The function by itself (45 chars):
```
m(){int (*a[])()={m,exit};i++;(*a[i>999])();}
```
A compilable, working program:
```
#include <stdio.h>
#include <stdlib.h>
int i=0;
m(){int (*a[])()={m,exit};i++;printf("%i ",i);(*a[i>999])();}
int main()
{
  m();
}
```
[Answer]
## Haskell, 33 chars
This is more like *inventing* the for loop, because there is no such nonsense in Haskell :P.
```
mapM_(putStr.(' ':).show)[0..999]
```
[Answer]
## GCC - 106 95 chars
```
#define FOR(i,l,h)auto F();L(F,l,h);int F(i)
L(int f(int),int l,int h){l<=h?f(l),L(f,l+1,h):0;}
```
Unlike the other C solutions where you have to declare a callback, this one does it for you automagically:
```
FOR(i, 1, 10) {
    printf("%d\n", i);
}
```
It works by using GCC's [nested function](http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html) extension. Namely, it forward-declares the nested function `F`, passes it to the looping function `L`, and then starts the definition of `F`, leaving the braces for the user to add.
One beautiful thing about nested functions in GCC is that they support downward funargs, meaning the illusion is nearly complete:
```
long n = 1;
FOR(i, 1, 10) {
    n *= i;
}
printf("%ld\n", n); // 3628800
```
There is one major caveat: if you use `FOR` twice in the same scope, you'll get a conflict (namely, it will compile, but all the `FOR` loops will share one loop body). To allow multiple FOR loops in the same scope, we'll need 69 65 more characters:
**175 160 chars:**
```
#define FOR(i,l,h)F(i,l,h,__COUNTER__)
#define F(i,l,h,f)auto N(f)();L(N(f),l,h);int N(f)(i)
#define N(n)F##n
L(int f(int),int l,int h){l<=h?f(l),L(f,l+1,h):0;}
```
[Answer]
## C, 21 characters
```
f(){if(c++<999)f();}
```
For example:
```
#include <stdio.h>
int c = 0;
f()
{
    printf("%d ", c);
    if (c++<999) f();
}
int main(void)
{
    f();
}
```
Outputs:
```
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 ... 998 999
```
[Answer]
## C# — no recursion, no goto
(using the Y combinator from lambda calculus)
```
class Program
{
    delegate Func<TInput, TResult> Lambda<TInput, TResult>(Lambda<TInput, TResult> f);
    static Func<TInput, TResult> Y<TInput, TResult>(Func<Func<TInput, TResult>, Func<TInput, TResult>> f)
    {
        Lambda<TInput, TResult> y = r => n => f(r(r))(n);
        return y(y);
    }
    static void Main()
    {
        Func<int, int> fibonacci = Y<int, int>(f => n => n > 1 ? f(n - 1) + f(n - 2) : n);
        Func<int, int> factorial = Y<int, int>(f => n => n == 0 ? 1 : n * f(n - 1));
        // Executes “fibonacci” 10 times, yielding 55
        Console.WriteLine(fibonacci(10));
        // Executes “factorial” 5 times, yielding 120
        Console.WriteLine(factorial(5));
    }
}
```
[Answer]
## x86 assembly, ~~12~~ 11 bytes' worth of instructions
```
66 31 c0                xor    %ax,%ax
<body>                ; involving %ax
66 40                   inc    %ax
66 3d  e8 03            cmp    $1000,%ax
75 ??                   jne    <body>
```
[Answer]
### Yet another Scala variant
Since Scala allows to use non-ASCII characters, we can implement real for :) (`o` is cyrillic).
```
def fоr(s:Unit,c: ⇒Boolean,e: ⇒Unit)(b: ⇒Unit):Unit=if(c){b;e;fоr(0,c,e)(b)}
```
Test:
```
var i:Int = _
fоr (i = 0, i < 1000, i += 1) {
  print(i + " ")
}
```
[Answer]
## Ruby 1.9 - 51 characters
```
def f a,b,c,&d
a[]
k=->{d[];c[];redo if b[]}
k[]end
```
This is a lot larger than other entries, but I think it captures the essence of the question better. In effect this allows you to write code almost exactly like the example:
```
def f a,b,c,&d
a[]
k=->{d[];c[];redo if b[]}
k[]end
i = 0 # Have to pre-declare i to have the closures work properly
f(proc{ i = 0 }, proc{ i < 1000 }, proc{ i += 1}) do
  p i
end
# Been a long time since I've actually used for's so took a long
# time to think of a non-trivial use.
j, sum = 0, 0 # Pre-declare variables for the closures
goal = 1000
f(proc{ j = 1; sum = 1 }, proc{ sum < goal }, proc{ j += 1 }) do
  sum = sum * j
end
puts "The next largest factorial after #{goal} is #{j-1}! at #{sum}"
```
[Answer]
# JavaScript, 34 characters
This assumes the actual printing function is *not* part of the `for` loop.
parameterized recursion **(43)**:
```
function f(i,m,c){if (i<m){c();f(++i,m,c)}}
function f(i, max, callback)
{
  if (i<max)
  {
    callback();
    f(++i,max,callback);
  }
}
```
reverse recursion **(36)**:  
assumes `max >= 0`
```
function f(m,c){if(m){c()
f(--m,c)}}
function f(max,callback)
{
  if(max)
  {
    callback();
    f(--max,callback);
  }
}
```
ternary operator **(34)**
```
function f(m,c)
{m?c()&f(--m,c):0}
```
[Answer]
# C#, 70 57 characters
C# isn't the weapon of choice for code golf, but I thought I'd try it out:
```
void f(int i,Func<int,bool>j,int k){if(j(i)) f(i+k,j,k);}
```
This doesn't only perform the task of counting up to 1000; rather, it attempts to actually replicate `for` loop behavior for any task. That seemed somewhat closer to the intent of the challenge, but maybe that's just me.
Expanded:
```
void f(int i, Func<int, bool> j, int k)
{
    if (j(i))
    {
        f(i + k, j, k);
    }
}
```
Usage is very close to for-loop syntax:
```
f(0, i => i < 1000, 1);  
```
[Answer]
## Python
Specific case:
```
exec("print i,"+";")*1000
```
And in general:
```
exec("f"+";")*1000
```
where 'f' is your code. Proabably doesn't work for all cases.
[Answer]
**C: 33 chars** for the base for loop (assuming goto is allowed)
```
int i=0;s:if(i<1000){/`*code inside for loop here`*/i++;goto s;}
int i=0;s:if(i<1000){printf("%d ",i);i++;goto s;}
```
[Answer]
I shall bear great shame for this, but here it is in Linux shell:
```
cat -An /dev/urandom|head -n1000|cut -f1
```
40 characters.
[Answer]
## PowerShell 18
```
filter p{$i=$_;$i}
```
1 - 10
```
PS C:\> (1..100 | p)-join' '
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 6
4 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 
```
Yeah, it's completely useless and you have to rewrite the function to do anything useful. But isn't that kind of the point? :)
[Answer]
Here's your loop using Brainfuck, which is probably cheating:
```
,[.,]
```
[Answer]
# C (No recursion, no goto's)
```
#include <stdio.h>
int main()
{
    puts("0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999");
    return 0;
}
```
Completely according to the definition, isn't it?
[Answer]
## JavaScript - 39 characters in test case
**Chrome, Opera, and IE:** `eval(s="i<1e3&&eval(s,print(i++))",i=0)`. This fails with "call stack size exceeded" on Safari and "too much recursion" on Firefox.
**Firefox:** `(function f()i<1e3&&f(print(i++)))(i=0)`. This uses Mozilla's non-standard "expression closure" feature to eliminate a pair of curly braces.
**Note:** Change `print(i++)` to `alert(i++)` if you need to. You can change `1e3` to `100` to reduce the number of iterations for Safari.
[Answer]
## QBasic (24 characters)
```
1?i:i=i+1:IF i<1E3THEN 1
```
expands to:
```
1 PRINT i: i = i + 1: IF i < 1000! THEN 1
```
**Note:** This assumes that `i` still has its original value of 0.
[Answer]
## J, ?<10 chars
```
f^:1000
```
In J there are (almost) no loops; instead, one usually uses arrays and implicit loops through them. For example, to sum the integers 1..100, you apply (/) the "verb" plus (+) to the array 1..100 (i.101) 
```
+/i.101
5050
```
To display the numbers 0..99, we just construct the array:
```
i.100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 ...
```
`^:` is the "power" verb; `f^:1000` is something like `exec()*1000` in python.
[Answer]
## C#, 58 characters
**Update:** D'oh...appears this is a virtually identical answer to [Eelvex](https://codegolf.stackexchange.com/questions/1034/reinvent-the-for-loop/1052#1052) who beat me by a few minutes. 
Not very clever - just simple recursion in .NET.
```
void f(int c,int m){Console.Write(c+" ");if(c++<m)f(c,m);}
```
Or taking out the body of the "for loop" (35 characters):
```
void f(int c,int m)if(c++<m)f(c,m);
```
Allows to seed the initial value and the max value.
[Answer]
# Scala
Inspired from [Nemo157's answer](https://codegolf.stackexchange.com/questions/1034/reinvent-the-for-loop/1044#1044):
```
def myfor(test: =>Boolean, inc: =>Unit)(stmts: =>Unit) : Unit =
        if (test) {
                stmts
                inc
                myfor(test, inc)(stmts)
        }
```
And this can be used like this:
```
var i = 0
myfor(i<1000, i+=1) {
        print(i+" ")
}
```
Golfed (62) :
```
def f(t: =>Boolean,i: =>Unit)(s: =>Unit){if(t){s;i;f(t,i)(s)}}
```
---
Or:
```
def myfor[A](init: A, test: (A)=>Boolean, inc: (A)=>(A))(stmts: =>Unit) : Unit = 
        if (test(init)) {
                stmts
                myfor(inc(init), test, inc)(stmts)
        }
myfor[Int](0, _<10, _+1) {
        println("loop")
}
```
[Answer]
**Clojure**  
`(map #(print (str % " ")) (range 1 (inc 100)))`
Replace print with the function to execute.  
Use (inc 100) or 101 for the last value.
[Answer]
## Perl, 21 characters
```
map{print"$_ "}0..999
```
[Answer]
# Perl most simple - 18 chars (ok, cheating)
```
print"@{[0..999]}"
```
output: 
 0 1 2 3 ... 998 999 
but:
# Perl regex/goatse op (real pseudoloop) - 39 (16) chars
```
()="@{[0..999]}"=~/\d+(?{print"$& "})/g
```
### the 'base loop' beeing 16 chars
```
()=             =~/\d+(?{          })/g
```
output: 
 0 1 2 3 ... 998 999 
Regards
rbo
[Answer]
# Javascript - 86 chars
```
e=eval,n=function(j,k,c){if(e(j))e(k),c(),n(j,k,c)},f=function(i,j,k,c){e(i),n(j,k,c)}
```
Maybe not the shortest javascript solution, but it replicates iterator declaration, iterator manipulation as well as a looping condition.
Example use case:
```
f('a = 0', 'a < 9', 'a++', function() {
    console.log(a);
});
```
[Answer]
```
;; for (int index=1, result=1; !cmp(result, max); index=incr(index)) result=body(index,result);
((lambda (index result cmp max body incr)
   ((lambda (f n i)
      (if (cmp i max) n
          (f f (body i n) (incr i))))
    (lambda (f n i)
      (if (cmp i max) n
          (f f (body i n) (incr i)))) result index)) 1 1 > 1000 (lambda (i n) (printf "i:~a~nn:~a~n" i n) (* n i)) (lambda (x) (+ x 1)))
```
[Answer]
## LISP, 91 characters
```
(defun m(x)(if(= 1000(length x))x(m(append x(list(1+(car(last x))))))))
(mapcar #'f(m'(0)))
```
*It could be shorter with labels.*
Example usage:
```
(defun f(x) (format t "~a " x))
(mapcar #'f (m '(0)))
0 1 2 3 4 5 6 7 8 9 10 11 12 ...  997 998 999
```
[Answer]
bash:
```
echo {1..1000}
```
14 chars. 
[Answer]
## Python3 - 27 chars
```
any(map(print,range(1000)))
```
[Answer]
## 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.
]