Write a function

Question

I honestly can't believe this challenge does not already exist.

The challenge

Write a function.

The specifics

• Your program must define some sort of callable function. This includes anything commonly known as a function, a lambda function, or a subroutine. All of these types of callables will be referred to as a "function" in this post.

  1. Input to the function is optional and not required.

  2. A return value from the function is also optional and not required but control must return to the calling program.

• The function must be assigned to some sort of variable so that it is possible to be accessed at a later time. This includes indirect assignment (in most common languages where declaring a named function automatically adds the name into the current scope) and direct assignment (assigning an anonymous function to a variable directly).

• The function does not need to be named.

• The function must be created by you - you cannot just assign a default function from the language to a variable.

• None of the standard loopholes, please.

This is code-golf, so lowest score in bytes wins.

Answer 1

x86 / x64 machine code, 1 byte

c3

Assembly:

ret

Try it online! (nasm)

¯\_(ツ)_/¯

Answer 2

Jelly, 0 bytes

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A monadic link that returns its argument. Since it is the first function to appear in the script, it can be called using 1Ŀ.

Thanks to @lirtosiast for pointing out that a 0 byte link/function would work in Jelly.

I.e.

3,4,5 1Ŀ

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Answer 3

Javascript, 6 bytes

f=_=>0

Includes variable assignment. Not much to see here.

Answer 4

Python 3, 9 bytes

def f():1

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Answer 5

ZX Spectrum BASIC, 6 bytes

DEF FN f()=PI

Hex dump: CE 66 28 29 3D A7. CE is a 1-byte keyword for DEF FN (including the trailing space), while A7 is a 1-byte keyword for PI. Call using FN f(). Example program:

  10 PRINT FN f(): DEF FN f()=PI

Output:

3.1415927

Answer 6

R, 9 bytes

body(t)=0

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I think this complies with the rules. The function t takes no input and outputs 0. This works because there already exists a function called t (the transposition function) and it redefines the body of the function; it would not work with say body(a)=0 (no object called a) or body(F)=0 (F is a logical, not a function). I think it complies because it is still created by me: I am not reusing what the pre-defined function does, simply its name.

I don't think I've ever seen this used by R golfers, but there may be situations where it allows us to save a few bytes on challenges where we need a helper function.

A more standard solution would have been:

R, 13 bytes

f=function()0

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Function which takes no input and outputs 0. This is 1 byte shorter than the function which takes no input and outputs nothing, which would be

f=function(){}

If we try to define a function with no body (f=function()), R interprets this as an incomplete command (this might not be true in older versions of R).

As pointed out by OganM, we take this down to 11 bytes with

R, 11 bytes

function()0

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which technically complies with the challenge requirement that the function be assigned to some sort of variable, since it is (ephemerally) assigned to .Last.value.

Answer 7

Haskell, 3 bytes

o=9

This code defines a polymorphic function called o which takes one type parameter and one typeclass instance parameter. When this function is called, it takes the given typeclass instance, gets its fromInteger member, calls that member with the Integer value for 9, and returns the result.

Granted, what I just described is merely the behavior of the Haskell function 9, and my code merely defines a function called o which is equivalent to 9.

Now the only question is, is the 9 function "created by you," or is it "a default function from the language"?

I think that it is "created by you." My reason for saying this is that if you read the specification for Haskell, you will (I assume) find no mention of a 9 function anywhere. Instead, the specification states that you can create a number literal by stringing together one or more digits. Therefore, by writing a string of digits, I have written a function—even if I just so happen to have only used one digit.

Answer 8

Perl 6, 5 bytes

$!=!*

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Creates a Whatever lambda that returns the boolean not of its parameter, and assigns it to the variable $!.

Answer 9

C (gcc), 5 bytes

Defines a function f that takes no arguments and technically returns an undefined integer value.

f(){}

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Answer 10

Whitespace, 7 bytes

Creates a subroutine that returns control to the caller.

Explained in context:

[N
S S N
_Create_Label][N
T   N
_Return]

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Answer 11

[Wolfram Language (Mathematica)], 1 byte

This one is slightly questionable:

f

Defines f, which can be "called" e.g. by f[], which "returns" the expression f[]

Answer 12

Forth (gforth), 5 bytes

This is a function named f that does nothing.

: f ;

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In the TIO code, I added a footer of see f, which prints the definition of the function.

Answer 13

Lua, 8 bytes

f=load''

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Defines a (global) function f.

This uses Lua load function to compile given string which happens to be empty in our case (empty code is valid code) into function which does exactly what we wrote in its body: nothing.

For ones wondering, standard solution would be

function f()end

but this is longer (15 bytes).

Answer 14

POSIX sh, 6 bytes

s()(1)

Using curly braces requires one more character.

Answer 15

Java, 10 Bytes

this should match the rules of the challenge

void f(){}

Answer 16

Perl 5, 7 bytes

sub f{}

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Answer 17

Kotlin, 8 bytes

val f={}

An empty function stored in a variable f.
Call it using f() or f.invoke().

Answer 18

shortC, 1 byte

A

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Transpiles into this C:

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

Answer 19

C (gcc), 14 13 bytes

(*f)()=L"Ã";

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This defines a function f returning int and accepting an unspecified number (and type) of parameters, the machine code of which is contained within the string literal. The unicode character Ã (stored in memory as 0xc3 0x00 0x00 0x00 on a little endian machine) corresponds to the x86 ret instruction that returns from the function. Non x86 architectures may require different opcode(s) to return.

gcc may require the -zexecstack flag to avoid a segfault.

Answer 20

Tcl, 6 5 11 bytes

set f {_ ;}

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Including the assignment to the variable f as part of the bytecount to comply with rules. With this change, the more conventional definition below ties the one above for bytecount:

proc f _ {}

Answer 21

Ruby, 6 bytes

Proc called f which accepts no argument and returns nil.

f=->{}

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Answer 22

Haskell, 5 bytes

f x=0

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Answer 23

XSLT, 134 bytes

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"><xsl:template name="a"></xsl:template></xsl:stylesheet>

A template is the closest thing this language has to a function. It can definitely be called; it takes zero arguments and "returns" the empty string.

Answer 24

F# (.NET Core), 9 bytes

let f a=a

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Answer 25

Python 3, 10 bytes

f=lambda:0

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Answer 26

Pascal 23bytes

procedure A;begin end;

Answer 27

Rust, 6 characters

f=||0;

A closure (also called lambda) that takes no parameters and always returns 0.

(As far as I understand the challenge, only the assignment has to be included, the variable declaration not.)

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Answer 28

AppleScript, 10

on a()
end

Explained, compiled, and including invocation:

on a()    -- declare event handler "a"
end a     -- end declaration

-- invoke it:
a()

Answer 29

Japt, 2 bytes

_

Called as $U ($.

_ can be replaced with @, Ï, or È.

Try it

Answer 30

SmileBASIC (>=3), 9 bytes

DEF A
END

Function is called by A.

Answer 31

Wolfram Language (Mathematica), 2 bytes

#&

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Unfortunately, just & does not work (an anonymous function that does nothing).

Answer 32

Octave, 4 bytes

xkcd Random Number Generator

@()4

Assigns an anonymous function to the default return variable ans. Call using ans(<parameters>). Any number of input parameters are allowed.

Code length is a random number of bytes.

Sample run on ideone.

Answer 33

Runic Enchantments, 1 byte

B
>00B$',$$;

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The second line is in the footer on TIO as all it does is initialize the program and invoke the function, and print the return values thereof (that being a pointer to the next instruction after the return statement--utilizing vs. discarding these values normally distinguishes a function call with a return), and as such should not be included in the bytecount any more than static void main(int[] args) { f(); } would be.

Similarly it shows the function "being assigned to a variable" (that being its literal coordinates, 0,0) and "invoked later" at position 3,1. For example, this program invokes the same function after performing some other operations and does so at a different point in the code. Note that the IP does not change direction automatically and may result in unexpected behavior, so functions typically start with a directional command, however in golfing it is insured that the IP is already going in the desired direction, resulting in not needing the extra byte(s).

Abusing language features, 0 bytes

/   B̭
 >00/$',$$;

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The first line (blank) is the 0-byte function. The second acts as function call and return. The third line initializes the program and produces output.

I definitely don't think that this should count, but thought I'd at least include it after I realized that I could arrange things this way. If bytes were to be counted from B call to B call in order of program flow, the function contains 8 bytes (four spaces, one /, one B, and two bytes for the ̭ directional modifier).

Answer 34

dc, 2

[]

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This pushes a dc macro to the stack. I'm not sure if this is satisfies "The function must be assigned to some sort of variable" or not. If not, then it can be stored to a variable for 2 extra bytes:

dc, 4

[]sf

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Answer 35

Binary lambda calculus, 1 byte

0100_0010

In lambda calculus: (λf. _)(λx. x)

The underscore denotes where the rest of the program should go. The function can be accessed through its De Bruijn index.

Answer 36

Attache -R, 2 bytes

{}

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An empty lambda. This approach takes advantage of the -R flag, which automatically saves the results of the topmost expression as _1 (also accessible through _). It can be used later, but only by the next expression which does not create a topmost expression. Usually, the next line.

Attache, 5 bytes

f:={}

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A more conventional approach. Saves an empty lambda to the variable f.

Attache, 6 bytes

f[]:=0

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Another conventional approach. Defines a named function f with no arguments, returning 0.

Answer 37

C#, 10 Bytes

Same as Java.

void f(){}

Answer 38

Commodore 64 Basic, 13 bytes

1DEFFNI(X)=X

The identity function. This, or any other function with a 1-byte body, is the shortest possible function in C64 Basic.

(Oddly, the empty function is considered a valid function by the C64 interpreter. But since actually calling it generates a runtime syntax error, it fails the "control must return" criterion.)

Answer 39

Swift, 8 bytes

let f={}

Stores in f a void function with no parameters.

Answer 40

Inform 7, 10 bytes

To x:stop.

This defines a "phrase" (the simplest form of callable function), which does nothing and returns. It can then be called by name:

When play begins, x.

Answer 41

Inform 6, 5 bytes

[f;];

The syntax for defining a routine in Inform 6 looks something like this:

[ name arg1 arg2 ;
    contents;
    return;
];

So [f;]; defines a routine named f which takes no arguments and does nothing.

Answer 42

Zozotez: 8

(:'q(\))
;; test 
(q) ; ==> NIL

Explanation:

• : is set
• 'q is the quoted symbol (the binding) q
• \ is lambda so (\) is short for (\ () ())

Common Lisp: 11

(defun q())
;; test 
(q) ; ==> NIL

R5RS/R6RS/R7RS Scheme: 12

(define(q)1)
;; test 
(q) ; ==> 1

Answer 43

Clojure, 10 bytes

Returns nil.

(defn f[])

Answer 44

CJam, 4 bytes

{}:F

Call it with F.

If just leaving a function on the stack is enough, then we can remove 2 bytes:

{}

Answer 45

Lua, 15 bytes

s=function()end

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Answer 46

C++14, 12 bytes

Empty lambda with no params

auto f=[]{};

Answer 47

Gema, 4 characters

f:=0

Actually a domain, which is a bit like namespace, but in Gema is the way to define both new pattern arguments and new functions.

(I guess the function's result could be nothing, but on f:= the interpreter segfaults. ☹)

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Answer 48

jq, 8 characters

def f:0;

A function that takes no parameters and always returns 0.

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Answer 49

R + dplyr, 20 bytes

library(dplyr)
.%>%.

Try it at RDRR!

Returns a functional sequence, the identity function.

Much longer than the other R answer but interesting in its own right.

Answer 50

Pyret, 7 bytes

a=_ + 0

Returns exactly what is passed to it. Underscore paired with an operand implicitly makes a function.

Answer 51

PowerShell, 0 bytes

Try it online!

You can save this code as a file with .ps1 extension (for example, f.ps1) and call it .\f.ps1. You can directly call this function from another code as scriptblock &{}. The function is inside the brackets.

Answer 52

REXX, 0 bytes

A REXX program may call another REXX program as an external function. Given an empty file as above, saved as f.rexx, you may call it from another program as:

call f

Or, if you're unconcerned by the difference between proper functions and subroutines, call it as:

f()

REXX, 8 bytes

f:return

This is a minimal procedure when called from within the same program. Call using call f or f() if you're not concerned about the philosophical difference between functions and procedures.

Answer 53

Commodore C64 BASIC, 30 BASIC bytes (tokens) used.

 0pO785,210:pO786,255:?usr(0)

This sets the USR BASIC memory pointer to 0xffd2 in the Kernal, which outputs a character on the current device (device 3 being the screen, set to device 4 or 5 and the output is to a printer, and 8 - 15 will be a disk drive, 1 is for tape).

You may therefore write your own machine code function that returns to BASIC if you put the memory location of your routine as above at location 785 (0x0311) as low-byte/high-byte. This must always be 16 bits.

Answer 54

Commodore 64 Basic, 9 bytes

You call the subroutine by GOSUB "\line number" and returns to the caller by RETURN. The function can be accessed anytime by calling the same line number, but the control should always return.

0reT   //Program continues after last Gosub executed
8goS0  //Call subroutine at line number 0

To execute this smallest program type: RUN8.

This program use tokens similarly to Shaun's answer.

Some facts of this program:

• There is no input to the actual function, but the function can access global variables.
• There is no return value from the function.
• The function has no name.
• The function is assigned a 16-bit variable that represents the basic line number (of low and high byte order).

This is the smallest I can think of, but of course expanding the number of digits in the line numbers will acually increase the codesize of the basic program.

For an demonstration with text-output, run this program by typing RUN8:

0 PRINT "INSIDE SUBROUTINE" : RETURN
8 PRINT "CALLING SUBROUTINE" : GOSUB 0
10 PRINT "RETURNED FROM SUBROUTINE"

Answer 55

33, 2 bytes

{}

The name of a function is whatever is in the destination string when the function is defined. Since the string registers are initialised empty when the program starts, this is valid and callable.

Answer 56

GolfScript, 5 bytes

{}: ;

This assigns a no-op to a space. In order to call the function, type a space.

Answer 57

Keg, 4 bytes

@a|@

To call the function:

@a@

This is unimplemented, but it is in the documentation.

Answer 58

Pip, 4 bytes

a:{}

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Pip, 0 bytes?

I don't know if this counts but the empty program in Pip is a function. It can be called by (f). If not then the 1 byte program a should count

Answer 59

Pari/GP, 5 bytes

f()=0

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Answer 60

Agda, 22 chars

Surprisingily difficult because of the required type signature and the lack of a preimported anything.

f : Set → _
f x = Set

Answer 61

BFASM / asm2bf, 9 bytes

lbl 1
ret

It builds to following brainfuck code (omitting boilerplate):

]>+<<+<<[>>->+<<<-]>>>[<<<+>>>-]<[->+<<[>>>-<<+<-]>[<+>-]>>[<->[-]]<[<<<+>>>-
]<]>>[-]<<<<[>>+>+<<<-]>>[<<+>>-]>[[-]>>>>>><<<<<<<<<[-]>[-]>>>>>>>>>>>>>>>[-
]>[>>]<<->[<<<[<<]>+>[>>]>-]<<<[<<]>[<<<<<<<<<<<<<<<+>>>>>>>>>>>>>>>-]<<<<<<<
[-]<<<<<<]<<<[>>+>+<<<-]>>[<<+>>-]>[[-]

Answer 62

Zsh, 5 bytes

Anonymous function... Try it online!

()(1)