In this task, the goal is to create the simplest possible program that is still considered "correct."

Programming Languages

Agena

Actually nothing is valid code, too. <lang agena></lang>

ALGOL 68

Brief form

BOLD form

AppleScript

An empty .scpt file is considered the smallest runnable code, but the following would also be acceptable. <lang applescript>return</lang>

Argile

The empty string or file are valid and do nothing. <lang Argile></lang>

AutoHotkey

An empty script would be enough. Adding "#Persistent" makes it persistent. <lang AutoHotkey>#Persistent </lang>

AutoIt

An a single comment can be considered a valid program that does nothing. <lang AutoIt>;nothing</lang>

AWK

The empty string (or file) is recognised as valid program that does nothing.

The program

is the simplest useful program: like the UNIX command 'cat', it prints every line of the files given as arguments, or (if no arguments are given) the standard input.

BASIC

Works with: QBasic

Batch File

An empty batch file is syntactically correct and does nothing.

Befunge

The halt command @ is required because code wraps around. An empty file would be an infinite loop.

Brainf***

Empty program

Note: this works as all non-instruction characters are considered comments. Alternatively, a zero-byte file also works.

Clean

module Empty

Start world = world

Compile the project with No Console or No Return Type to suppress printing of the value of the world.

Clojure

An empty file is the simplest valid Clojure program.

D

Works with: DMD

Works with: GDC

E

The shortest possible program:

This is equivalent to:

null

eC

or

class EmptyApp : Application
{
   void Main()
   {

   }
}

Erlang

An empty module:

-module(empty).

An empty Erlang script file (escript):


main(_) -> 1.

eSQL

CREATE COMPUTE MODULE ESQL_Compute
 CREATE FUNCTION Main() RETURNS BOOLEAN
 BEGIN
   RETURN TRUE;
 END;
END MODULE;

Factor

If you want to deploy a stand-alone application, that doesn't suffice though. Here's another version.

<lang factor>IN: rosetta.empty

main ( -- ) ;

MAIN: main</lang>

Forth

<lang forth></lang> For a Forth script to be used from a shell, you usually want the last command to be BYE in order to exit the interpreter when finished. <lang forth>bye</lang>

Fortran

end

Gema

An empty program will copy input stream to output stream unchanged. <lang gema></lang>

Go

<lang go>package main func main() { }</lang>

Haskell

Standard: Haskell 98

The simplest possible program is a single module using the implicit module header "module Main(main) where", and defining the action main to do nothing:

main = return ()

The simplest possible module other than Main is one which contains no definitions:

module X where {}

haXe

class Program {
   static function main() {
   }
}

Unlike most languages haXe doesn't have arguments in the main function because it targets different platforms (some which don't support program arguments, eg: Flash or Javascript). You need to use the specific libraries of the platform you are targeting to get those.

HicEst

<lang hicest>END ! looks better, but is not really needed</lang>

Icon and Unicon

Icon

<lang Icon>procedure main() # a null file will compile but generate a run-time error for missing main end</lang>

Unicon

This Icon solution works in Unicon.

IDL

end

Io

J

<lang j></lang> It returns itself: <lang j> -: ". 1 </lang>

Java

Works with: Java version 1.5+

<lang java>public class EmptyApplet extends java.applet.Applet {

   @Override public void init() {
   }

}</lang>

<lang java>public class EmptyMainClass {

   public static void main(String... args) {
   }

}</lang>

The "..." basically means "as many of these as the programmer wants." Java will put multiple arguments into an array with the given name. This will work for any method where an array is an argument, but with a twist. A call can be made like this:

<lang java>method(arg0, arg1, arg2, arg3)</lang>

All of the args will be put into an array in the order they were in the call.

Works with: Java version 1.0+

<lang java>public class EmptyMainClass {

   public static void main(String[] args) {
   }

}</lang>

<lang java>public class EmptyApplet extends java.applet.Applet {

   public void init() {
   }

}</lang>

@Override - Indicates that a method declaration is intended to override a method declaration in a superclass. If a method is annotated with this annotation type but does not override a superclass method, compilers are required to generate an error message. It's present from JDK 5.0 (1.5.0) and up.

Actually this is not strictly correct. The smallest possible correct program in Java is an empty source file.

JavaScript

The empty file is a valid program.

Joy

!/usr/local/bin/joy.exe

quit. </lang>

The RCE(P)L of JOY reads a program -- which looks like a sentence, ending in a full stop -- compiles it, executes it and optionally prints the top of the stack. The only way to exit this loop properly is to call quit, which is equivalent to exit(0); in C.

Liberty BASIC

Lisp

Most Lisp dialects, including Common Lisp, will accept no text (no forms) as a valid program. <lang lisp></lang>

Logo

<lang logo></lang> or end a standalone script with "bye" <lang logo>

! /usr/local/bin/logo

bye </lang>

LSE64

As with Forth, an empty file is the shortest program. To exit the interpreter at the end of a loaded file:

bye

Lua

M4

Mathematica

MATLAB

<lang Matlab> function [varargout] = emptyprogram(varargin) </lang>

MAXScript

An empty MAXScript file returns "OK" on execution

Metafont

MMIX

Modula-3

<lang modula3>MODULE Main;

BEGIN END Main.</lang>

MUMPS

The empty file is a valid program.

NewLISP

Nimrod

Objeck

<lang objeck> bundle Default {

 class Empty {
   function : Main(args : String[]) ~ Nil {
   }

} </lang>

Objective-C

Works with: gcc version 4.0.1

<lang objc>int main(int argc, const char **argv) {

   return 0;

}</lang>

The minimal empty Cocoa/OpenStep application, useful as life-support for many examples given at RosettaCode, is

<lang objc>#import <Cocoa/Cocoa.h>

int main( int argc, const char *argv[] ) {

 NSAutoreleasePool *pool;
 
 pool = [[NSAutoreleasePool alloc] init];
 NSApp = [NSApplication sharedApplication];
   
 [pool release];
 return 0;

}</lang>

OCaml

Works with: Ocaml version 3.09

Actually, the smallest possible correct program in OCaml is an empty source file.

Octave

An empty text file can be a valid empty program, but since Octave has the concept of "function file" (a file containing a single function; the file is automatically loaded when a function with the same name of the file, save for the extension, is called, and the first function present in the file is used), the name of the empty file matters. E.g. calling an empty file as isempty.m makes unusable the builtin isempty function.

Oz

REPL

The simplest program that can be evaluated in the REPL (Emacs mode) is the empty program. <lang oz></lang>

Accepted by compiler

The simplest 'program' that can be compiled is a file which contains a single expression. <lang oz>unit</lang> Such a 'program' cannot be executed, though.

Standalone

The simplest standalone program is a root functor that does not define anything. ("Functors" are first-class modules.) <lang oz>functor define

  skip

end</lang>

Pascal

<lang pascal>program ProgramName;

begin end.</lang>

The first line is not necessary in modern Pascal dialects. With today's most compilers, the empty program is just: <lang pascal>begin end.</lang>

Perl

Works with: Perl version 5.8.8

<lang perl>#!/usr/bin/perl

A program without a body will work too</lang>

The smallest possible program is an empty file (zero length). This requires you to specify the interpreter instead of relying on the shell's shebang magic, thus: perl empty.pl.

The smallest possible Perl one-liner is perl -e0.

Perl 6

In theory, an empty file is a valid Perl 6 program that does nothing. However, Synopsis 1 decrees "The perl interpreter will assume that it is being fed Perl 5 code unless the code starts with a 'class' or 'module' keyword, or you specifically tell it you're running Perl 6 code in some other way". So, a strictly specification-compliant implementation would interpret an empty file as Perl 5. Probably the shortest file that's unconditionally a Perl 6 program is

since it'll cause pre-6 perls to die with an appropriate error message.

PHP

An empty text file is a correct PHP program that does nothing.

PicoLisp

Pike

<lang pike>int main(){

  return 0;

}</lang>

PL/I

<lang PL/I> s: proc options (main); end; </lang>

PL/SQL

BEGIN
  NULL;
END;

Pop11

Pop11 has two compilers, incremental and batch compiler. For the incremental compiler one can use just empty program text (empty file), or a file containing nothing but a comment, e.g.

;;; This is a valid Pop11 program that does absolutely nothing.

The batch compiler generates an executable which starts at a given entry point, so one should provide an empty function. If one wants program that works the same both with incremental compiler and batch compiler the following may be useful:

compile_mode :pop11 +strict;
define entry_point();
enddefine;

#_TERMIN_IF DEF POPC_COMPILING
entry_point();

Here the batch compiler will stop reading source before call to entry_point while incremental compiler will execute the call, ensuring that in both cases execution will start from the function entry_point.

PostScript

An empty file is a valid PostScript program that does nothing.

Following good programming practice, however, and to ensure that a PostScript printer will interpret a file correctly, one should make the first 4 characters of the file be

%!PS

If a particular version of the PS interpreter is needed, this would be included right there:

%!PS-2.0
% ...or...
%!PS-3.0
% etc

PowerShell

An empty text file is a correct Powershell script that does nothing.

PureBasic

An empty file is a correct PureBasic program that does nothing. <lang PureBasic></lang>

Python

An empty text file is a correct Python program that does nothing.

R

An empty text file is a valid empty program

Raven

An empty text file is an empty program.

REBOL

The header section is mandatory if you want it to be recognized as a REBOL program. It doesn't have to be filled in though: <lang REBOL>REBOL []</lang>

REXX

An empty file is a valid empty program; however, for some REXX implementation the first two characters must be /* (i.e. the first line must be a comment) in order to recognize the file as a REXX script: <lang rexx>/* empty */</lang>

Rhope

Works with: Rhope version alpha 1

Main(0,0)
|: :|

Ruby

An empty file is a valid Ruby program. However, in order to make it runnable on *nix systems, a shebang line is necessary: <lang ruby>#!/usr/bin/ruby</lang>

Scala

<lang scala>object emptyProgram {

   def main(args: Array[String]) {}

}</lang>

Scheme

Slate

<lang slate>
</lang>

SNUSP

$#

$ sets the instruction pointer (going right), and # halts the program (empty stack).

SNOBOL4

A valid program requires an end label. The shortest (virtually empty) program is then: <lang snobol>end</lang>

Standard ML

Actually, the smallest possible correct program in Standard ML is an empty source file.

Suneido

<lang Suneido>function () { }</lang>

Tcl

Nothing is mandatory in Tcl, so an empty file named nothing.tcl would be a valid "empty program".

Toka

For interpreted code, nothing is required, although bye is necessary for an empty script to exit (rather than wait for the user to exit the listener). Hence:

bye

Or, for a directly runnable script:

#! /usr/bin/toka
bye

For compiled code, the simplest program is an empty quote:

[ ]

Again, to exit the listener, you will still need user input if this is not followed with bye.

TI-83 BASIC

TI-89 BASIC

Prgm
EndPrgm

Trith

UNIX Shell

Works with: Bourne Shell

#!/bin/sh

Works with: Bourne Again SHell

#!/bin/bash

Unlambda

(See how i plays so many roles in unlambda?)

VBScript

An empty .vbs file is considered the smallest runnable code, but the following (a single apostrophe as comment marker) would also be acceptable (along with other non-executing instructions like option explicit.) <lang vb>'</lang>

Visual Basic .NET

Works with: Visual Basic .NET version 2005

<lang vbnet>Module General

   Sub Main()
   End Sub

End Module</lang>

X86 Assembly

Works with: NASM version Linux

<lang asm> section .text global _start

_start: mov eax, 1 int 0x80 ret

</lang>

Works with: MASM

<lang asm> .386 .model flat, stdcall option casemap:none

.code start: ret end start </lang>

XQuery

<lang xquery> . </lang> The dot selects the current context node and returns it unchanged.

XSLT

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
</xsl:stylesheet>

Add other namespaces to the stylesheet attributes (like xmlns:fo="http://www.w3.org/1999/XSL/Format") if you use them.

Since XSLT is XML, and <lang>transform</lang> is a synonym for <lang>stylesheet</lang>, the example above can be minified to:

<transform xmlns="http://www.w3.org/1999/XSL/Transform" version="1.0"/>

This stylesheet echoes the text content of an XML file. The shortest stylesheet without any output would be

<transform xmlns="http://www.w3.org/1999/XSL/Transform" version="1.0">
  <template match="/" />
</transform>

xTalk

Works with: HyperCard

on startup
  
end startup

Programming Languages

Brief form

BOLD form

Icon and Unicon

REPL

Accepted by compiler

Standalone

Markup Languages