Empty program

Empty program
You are encouraged to solve this task according to the task description, using any language you may know.

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

Programming Languages

Ada

Works with: GCC version 4.1.2

procedure Empty is 
begin 
   null; 
end;

Agena

Actually nothing is valid code, too.

Aime

The nil input is a valid program.

ALGOL 68

Brief form

~

BOLD form

SKIP

AmigaE

PROC main()
ENDPROC

AppleScript

An empty .scpt file is considered the smallest runnable code, but the following would also be acceptable.

return

Argile

The empty string or file are valid and do nothing.

AutoHotkey

An empty script would be enough. Adding "#Persistent" makes it persistent.

#Persistent

AutoIt

An a single comment can be considered a valid program that does nothing.

;nothing

AWK

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

The program

    1

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

10 END

Works with: ZX Spectrum Basic

On the ZX Spectrum, we can have a completely empty program with no lines. Here we attempt to run the empty program:

RUN

0 OK, 0:1

Batch File

An empty batch file is syntactically correct and does nothing.

But on windows 7 an empty .bat file is not recognized and thus a character must exist in it:

REM

BBC BASIC

In BBC BASIC an empty program is syntactically correct.

Befunge

@

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

Bracmat

An empty file is a valid program. However you need to load it, which requires a statement. In a Linux terminal, you could do

touch empty
bracmat 'get$empty'

In DOS, you can do

touch empty
bracmat get$empty

If we drop the requirement that the shortest program is stored in a file, we can do

bracmat ''

(Linux) or

bracmat ""

(Windows)

If two quotes to demarcate an empty string are counted as bigger than a single undemarcated non-empty expression, we can do

 bracmat .

The dot is a binary operator. So the input consists of three nodes: the operator and its lhs and rhs, both empty strings in this case. If three nodes is too much, consider a slightly bigger glyph, such as the hyphen, which is a prefix, not a binary operator:

 bracmat -

You also can start Bracmat without arguments, in which case it will run in interactive mode. Now press the Enter key. You have just run the shortest valid Bracmat program.

Brainf***

Empty program

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

Brlcad

Pressing enter from the mged prompt, just returns another prompt, so I suppose that is the smallest possible program. However, before we can draw anything we at least need to open a database:

opendb empty.g y

C

You'll notice that each example has an int return type, and returns 0. The meaning of the return value is system-dependent.

argc contains the number of arguments. argv is an array containing those arguments as null-terminated strings. These memory for these strings are maintained by the runtime, and don't need to be manually freed.

int main(int argc, char* argv[])
{
  return 0;
}

It's also possible to empty signature for main function.

Works with: gcc version 4.0.3

int main ()
{
  return 0;
}

In versions of C before C99, it was possible to skip return type of function if it was int. This isn't allowed anymore, but some compilers allow it in C89 compatibility modes.

main () {
  return 0;
}

C#

class Program
{
    static void Main()
    {
    }
}

C++

Works with: g++ version 4.0.3

int main ( int /*argc*/, char * * /*argv*/ ) 
{
 // Unused arguments should not be named
 // There are variations:
 // 1: main ''may'' explicitly return a value
 //    (other non-void-returning C++ functions ''must'' do so,
 //    but there's a special exception for main that falling off it
 //    without an explicit return is equivalent to a "return 0;" at
 //    the end of the main function)
 // 2: The arguments may be omitted entirely
}

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.

COBOL

This example was written by a novice in COBOL. If you are familiar with COBOL, please review and edit this example and remove this message. If the example does not work and you cannot fix it, replace this message with {{incorrect|COBOL|description of problem as you see it}}. If the code is correct but unidiomatic and you cannot fix it, replace this message with {{improve|COBOL|description of how it should be improved}}.

Experimented with OpenCOBOL and found this to be the minimal source code that compiles and runs.

 
Identification division.
Program-id. minimal.
 

D

void main() {}

Dart

main() {
}

Delphi

See Pascal

E

The shortest possible program:

This is equivalent to:

null

eC

or

class EmptyApp : Application
{
    void Main()
    {
 
    }
}

Eiffel

A file called root.e:

class
    ROOT
 
create
    make
 
feature
    make
        do
 
        end
end

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;

EGL

General program

 
package programs;
 
program Empty_program type BasicProgram {}
	function main()
	end
end
 

Rich UI handler (but also without 'initialUI = [ ui ], onConstructionFunction = start' it would have been valid.)

package ruihandlers;

import com.ibm.egl.rui.widgets.Div;

handler Empty_program type RUIhandler {initialUI = [ ui ], onConstructionFunction = start}
	ui Div{};
	
	function start()
	end	
end

F#

F# has an interactive mode and a compiled mode. The interactive interpreter will accept an empty file so the shortest valid program is an empty zero-length file with the .fsx extension.

An empty compiled program is:

[<EntryPoint>]
let main args = 0

Factor

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

IN: rosetta.empty
: main ( -- ) ;
MAIN: main

Falcon

>

Prints an empty line.

>>

Prints nothing.

Fantom

class Main
{
  public static Void main () {}
}

Fish

Actually the shortest valid program is a space (not empty file!), which is an infinite loop, though. (It keeps looping around)

An empty program is invalid; the interpreter will give an error.
The shortest program that will actually finish is a ;, which will end the program immediately:

;

Forth

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.

bye

Fortran

       end

friendly interactive shell

Empty programs are valid, but are useless.

Frink

Empty programs are valid.

Gecho

Empty programs are valid.

Gema

An empty program will copy input stream to output stream unchanged.

Go

package main
func main() { }

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

END ! looks better, but is not really needed

HQ9+

An empty file is a valid HQ9+ program that does nothing.

Icon and Unicon

procedure main()   # a null file will compile but generate a run-time error for missing main
end

IDL

end

Intercal

PLEASE GIVE UP

J

It returns itself:

   '' -: ". ''
1

Java

Works with: Java version 1.5+

public class EmptyApplet extends java.applet.Applet {
    @Override public void init() {
    }
}

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

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:

method(arg0, arg1, arg2, arg3)

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

Works with: Java version 1.0+

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

public class EmptyApplet extends java.applet.Applet {
    public void init() {
    }
}

@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.

KonsolScript

function main() {
 
}

Lang5

exit

Liberty BASIC

end

Lilypond

According to the manual, all lilypond programs should contain a version statement expressing the minimum version number. If this is missing then a warning will be emitted.

\version "2.6.12"

An input file should really have a basic structure as follows. The compiler automatically adds some of the structure components if they are not present in the source code. However, explicit definition should be used to prevent the compiler from creating unwanted contexts (which can cause side effects):

\version "2.16.2"
 
\header {
 
}
 
\book {
  \score {
    \new Staff {
      \new Voice {
 
      }
    }
    \layout {
 
    }
  }
}

Lisp

Most Lisp dialects, including Common Lisp, will accept no text (no forms) as a valid program.

Logo

or end a standalone script with "bye"

#! /usr/local/bin/logo
 
bye

LSE64

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

bye

MATLAB

 function [varargout] = emptyprogram(varargin) 

Maxima

block()$

MAXScript

An empty MAXScript file returns "OK" on execution

Metafont

end

МК-61/52

С/П

MMIX

	LOC	#100
Main	TRAP	0,Halt,0	// main (argc, argv) {}

Modula-2

MODULE Main;
 
BEGIN
END Main.

Modula-3

MODULE Main;
 
BEGIN
END Main.

MUMPS

The empty file is a valid program.

Nemerle

Compiles with warnings:

null

Compiles without warnings (so, more correct):

module Program
{
    Main() : void
    {
    }
}

NetRexx

The following two samples both generate valid programs.

This minimal example requires that the file be named to match the class:

class empty

This example will generate it's class based on the file name:

method main(args = String[]) static

NewLISP

; 

Objeck

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

Objective-C

Works with: gcc version 4.0.1

int main(int argc, const char **argv) {
    return 0;
}

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

#import <Cocoa/Cocoa.h>
 
int main( int argc, const char *argv[] )
{
  NSAutoreleasePool *pool;
 
  pool = [[NSAutoreleasePool alloc] init];
  NSApp = [NSApplication sharedApplication];
 
  [pool release];
  return 0;
}

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.

OxygenBasic

The smallest possible program is a single space character:

Oz

REPL

The simplest program that can be evaluated in the REPL (Emacs mode) is the empty program.

Accepted by compiler

The simplest 'program' that can be compiled is a file which contains a single expression.

unit

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.)

functor
define
   skip
end

Pascal

program ProgramName;
 
begin
end.

The first line is not necessary in modern Pascal dialects. With today's most compilers, the empty program is just:

begin end.

Perl

Works with: Perl version 5.8.8

#!/usr/bin/perl
1;

#!/usr/bin/perl
exit;

#!/usr/bin/perl
# A program without a body will work too

#!/usr/bin/perl

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

The empty program is valid and does nothing but return a successful exit code.

It is also possible to just specify that the program is written in Perl6:

use v6;

or, for relax mode (not yet implemented in rakudo, though):

v6;

or even:

6;

PHP

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

PicoLisp

(de foo ())

PIR

The :main pragma indicates that a subroutine is the program's entry point. However, if a subroutine is the first (or only, which would also have the effect of making it the first) routine in the program, Parrot will use that. So we may comfortably omit it in this case.

.sub empty_program
.end

Pike

int main(){}

PL/I

s: proc options (main);
end;

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.

PSQL

EXECUTE BLOCK
AS
BEGIN
END

ProDOS

This is an acceptable program:

IGNORELINE

But also you could include a delimiter character recognized by the compiler/interpreter:

;

PureBasic

An empty file is a correct PureBasic program that does nothing.

Python

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

R

An empty text file is a valid empty program

Racket

The following shows an empty program in Racket's default language. Other Racket languages may impose different conditions on the empty program.

 
#lang racket
 

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:

rebol []

Retro

An empty file is the smallest valid program.

To save an application doing nothing, you need to do a bit more work though:

&bye is boot

REXX

version 1

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:

/* empty */

version 2

/**/

version 3

REXX on MVS/TSO requires REXX to be in the first line:

 
/* REXX */
 

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:

#!/usr/bin/env ruby

Scala

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

Seed7

$ include "seed7_05.s7i";
 
const proc: main is noop;

Smalltalk

[]

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:

end

Standard ML

;

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

Suneido

function () { }

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

TUSCRIPT

$$ MODE TUSCRIPT

UNIX Shell

Works with: Bourne Shell

#!/bin/sh

Works with: Bourne Again SHell

#!/bin/bash

Unlambda

i

(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.)

'

VHDL

Compiled and simulated by Modelsim:

entity dummy is
end;
 
architecture empty of dummy is
begin
end;

Visual Basic .NET

Works with: Visual Basic .NET version 2005

Module General
    Sub Main()
    End Sub
End Module

X86 Assembly

Works with: NASM version Linux

section .text
	global _start
 
	_start:
		mov eax, 1
		int 0x80
		ret

Works with: MASM

.386
.model flat, stdcall
option casemap:none
 
.code
start:
ret
end start

XPL0

An empty file compiles and builds an EXE file with a single RET instruction, but of course does nothing when executed.

XQuery

.

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">
   <!-- code goes here -->
</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 transform is a synonym for stylesheet, 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

XUL

 
<?xml version="1.0"?>
 

Yorick

An empty file is valid and does nothing.

Markup Languages

HTML

HTML 5, section 11.1.2.4 Optional tags, allows to omit html, head and body tags. The implicit body element can be empty, but the implicit head element must contain a title element, says section 4.2.1 The head element. There seems no rule against an empty title. Therefore, the shortest correct HTML document is:

<!DOCTYPE html><title></title>

The shortest correct XHTML document is:

<html xmlns="http://www.w3.org/1999/xhtml"><head><title /></head><body /></html>

plainTeX

\bye

LaTeX

\documentclass{article}
\begin{document}
\end{document}