Function definition

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Task
Function definition
You are encouraged to solve this task according to the task description, using any language you may know.

A function is a body of code that returns a value. The value returned may depend on arguments provided to the function.

Write a definition of a function called "multiply" that takes two arguments and returns their product. (Argument types should be chosen so as not to distract from showing how functions are created and values returned).

See also:Function prototype

Contents

[edit] 8051 Assembly

Like other assembly languages, 8051 doesn't have functions but instead has symbolic references to code. Function arguments are passed via registers decided on beforehand.

ORG RESET
mov a, #100
mov b, #10
call multiply
; at this point, the result of 100*10 = 1000 = 03e8h is stored in registers a and b
; a = e8
; b = 03
jmp $
 
multiply:
mul ab
ret

[edit] ACL2

(defun multiply (a b) (* a b))

[edit] ActionScript

function multiply(a:Number, b:Number):Number {
return a * b;
}

[edit] Ada

function Multiply (A, B : Float) return Float;

and an implementation of:

function Multiply (A, B : Float) return Float is
begin
return A * B;
end Multiply;


The Ada 2012 standard provides an even simpler way to define and implement functions:

function Multiply(A, B: Float) return Float is (A * B);


Ada supports generic functions which can take generic formal parameters like the numeric type to use:

generic
type Number is digits <>;
function Multiply (A, B : Number) return Number;

implemented as:

function Multiply (A, B : Number) return Number is
begin
return A * B;
end Multiply;

To use this, you need to instantiate the function for each type e.g.

 
with Multiply;
...
function Multiply_Integer is new Multiply(Number => Integer);
use Multiply_Integer; -- If you must
 
type My_Integer is Range -100..100;
function Multiply_My_Integer is new Multiply(My_Integer);
 

[edit] Aime

real
multiply(real a, real b)
{
return a * b;
}

[edit] ALGOL 68

PROC multiply = ( LONG REAL a, b ) LONG REAL:
(
a * b
)

[edit] AmigaE

PROC my_molt(a,b)
-> other statements if needed... here they are not
ENDPROC a*b -> return value
 
-> or simplier
 
PROC molt(a,b) IS a*b
 
PROC main()
WriteF('\d\n', my_molt(10,20))
ENDPROC

[edit] APL

       multiply  ←  ×

Works on arrays of any rank (any number of dimensions): atoms, lists, tables, etc.

[edit] AppleScript

on multiply(a, b)
return a * b
end

[edit] Applesoft BASIC

Applesoft BASIC functions are unary meaning they only take one argument. As the task asks for a multiply function which takes two arguments this poses a problem. To get around this, the multiply function MU takes one argument as the offset into an array of parameters.

Function names in Applesoft BASIC can be longer than two characters but only the first two characters are significant. Function names cannot contain any keywords.

10  DEF  FN MULTIPLY(P) =  P(P) * P(P+1)
20 P(1) = 611 : P(2) = 78 : PRINT FN MULTIPLY(1)
47658

[edit] Argile

use std
.: multiply <real a, real b> :. -> real {a * b}

with a macro and a variable number of parameters:

use std
=: multiply <real a> [<real b>...] := -> real {Cgen a (@@1 (Cgen " * " b))}

[edit] AutoHotkey

MsgBox % multiply(10,2)
 
multiply(multiplicand, multiplier) {
Return (multiplicand * multiplier)
}

[edit] AutoIt

#AutoIt Version: 3.2.10.0
$I=11
$J=12
MsgBox(0,"Multiply", $I &" * "& $J &" = " & product($I,$J))
Func product($a,$b)
Return $a * $b
EndFunc

[edit] AWK

function multiply(a, b)
{
return a*b
}
BEGIN {
print multiply(5, 6)
}

[edit] BASIC

Works with: QBasic
DECLARE FUNCTION multiply% (a AS INTEGER, b AS INTEGER)
 
FUNCTION multiply% (a AS INTEGER, b AS INTEGER)
multiply = a * b
END FUNCTION

[edit] Batch File

Windows batch files only have procedures, not functions. Instead, environmental variables can be used as a global shared state.

@ECHO OFF
SET /A result = 0
CALL :multiply 2 3
ECHO %result%
GOTO :eof
 
:multiply
SET /A result = %1 * %2
GOTO :eof
 
:eof

[edit] BBC BASIC

BBC BASIC supports both single-line and multi-line function definitions. Note that the function name must begin with FN.

Single-line function:

PRINT FNmultiply(6,7)
END
 
DEF FNmultiply(a,b) = a * b

Multiline function:

DEF FNmultiply(a,b)
LOCAL c
c = a * b
= c

[edit] bc

Works with: GNU bc
define multiply(a, b) { return a*b }
 
print multiply(2, 3)

[edit] Boo

def multiply(x as int, y as int):
return x * y
 
print multiply(3, 2)

[edit] Bracmat

multiply=a b.!arg:(?a.?b)&!a*!b;
out$multiply$(123456789.987654321); { writes 121932631112635269 to standard output }

[edit] Brat

multiply = { x, y | x * y }
 
p multiply 3 14 #Prints 42

[edit] C

double multiply(double a, double b)
{
return a * b;
}

[edit] Macros

Macros can be defined at the top of a program and the compiler will replace the function calls with the function itself before compiling the program (the source file will not change).

#define MULTIPLY(X, Y) ((X) * (Y))

Parentheses should be added around parameters in the function definition to avoid order of operations errors when someone uses the macro as such:

x = MULTIPLY(x + z, y);

A program with that call would be compiled as if this were coded instead:

x = ((x + z) * (y));

Another advantage of macros is that they work with all types alike. For example, the above macro can be used both to multiply double values (like the function above), and to multiply int values (giving an int, which the function doesn't).

[edit] C#

static double multiply(double a, double b)
{
return a * b;
}

Anonymous function:

Func<double, double, double> multiply = ((a,b) => a*b);

[edit] C++

C++ functions basically are the same as in C. Also macros exist, however they are discouraged in C++ in favour of inline functions and function templates.

An inline function differs from the normal function by the keyword inline and the fact that it has to be included in every translation unit which uses it (i.e. it normally is written directly in the header). It allows the compiler to eliminate the function without having the disadvantages of macros (like unintended double evaluation and not respecting scope), because the substitution doesn't happen at source level, but during compilation. An inline version of the above function is:

inline double multiply(double a, double b)
{
return a*b;
}

If not only doubles, but numbers of arbitrary types are to be multiplied, a function template can be used:

template<typename Number>
Number multiply(Number a, Number b)
{
return a*b;
}

Of course, both inline and template may be combined (the inline then has to follow the template<...>), but since templates have to be in the header anyway (while the standard allows them to be compiled separately using the keyword export, almost no compiler implements that), the compiler usually can inline the template even without the keyword.


[edit] Clay

multiply(x,y) = x * y;


[edit] Clojure

(defn multiply [x y]
(* x y))
 
(multiply 4 5)

Or with multiple arities (in the manner of the actual * function):

(defn multiply
([] 1)
([x] x)
([x y] (* x y))
([x y & more]
(reduce * (* x y) more)))
 
(multiply 2 3 4 5) ; 120

[edit] COBOL

In COBOL, multiply is a reserved word, so the requirements must be relaxed to allow a different function name. The following uses a program:

Works with: OpenCOBOL
       IDENTIFICATION DIVISION.
PROGRAM-ID. myTest.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 x PIC 9(3) VALUE 3.
01 y PIC 9(3) VALUE 2.
01 z PIC 9(9).
PROCEDURE DIVISION.
CALL "myMultiply" USING
BY CONTENT x, BY CONTENT y,
BY REFERENCE z.
DISPLAY z.
STOP RUN.
END PROGRAM myTest.
 
IDENTIFICATION DIVISION.
PROGRAM-ID. myMultiply.
DATA DIVISION.
LINKAGE SECTION.
01 x PIC 9(3).
01 y PIC 9(3).
01 z PIC 9(9).
PROCEDURE DIVISION USING x, y, z.
MULTIPLY x BY y GIVING z.
EXIT PROGRAM.
END PROGRAM myMultiply.

This example uses user-defined functions, which were added in COBOL 2002.

Works with: GNU Cobol version 2.0
       IDENTIFICATION DIVISION.
PROGRAM-ID. myTest.
ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
REPOSITORY.
FUNCTION myMultiply.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 x PIC 9(3) VALUE 3.
01 y PIC 9(3) VALUE 2.
PROCEDURE DIVISION.
DISPLAY myMultiply(x, y).
STOP RUN.
END PROGRAM myTest.
 
IDENTIFICATION DIVISION.
FUNCTION-ID. myMultiply.
DATA DIVISION.
LINKAGE SECTION.
01 x PIC 9(3).
01 y PIC 9(3).
01 z pic 9(9).
PROCEDURE DIVISION USING x, y RETURNING z.
MULTIPLY x BY y GIVING z.
EXIT FUNCTION.
END FUNCTION myMultiply.

[edit] Coco

As CoffeeScript. In addition, Coco provides some syntactic sugar for accessing the arguments array reminiscent of Perl's @_:

multiply = -> @@0 * @@1

Furthermore, when no parameter list is defined, the first argument is available as it:

double = -> 2 * it

[edit] CoffeeScript

multiply = (a, b) -> a * b

[edit] ColdFusion

<cffunction name="multiply" returntype="numeric">
<cfargument name="a" type="numeric">
<cfargument name="b" type="numeric">
<cfreturn a * b>
</cffunction>

[edit] Common Lisp

Common Lisp has ordinary functions and generic functions.

[edit] Ordinary Functions

Ordinary functions operate on the values of argument expressions. Lisp functions terminate by returning one or more values, or by executing a non-local dynamic control transfer, in which case values are not returned.

(defun multiply (a b)
(* a b))
 
(multiply 2 3)

[edit] User-Defined Compiler Optimization of Functions

In Lisp we can express optimizations of calls to a function using compiler macros. For instance, suppose we know that the multiply function, which may be in another module, simply multiplies numbers together. We can replace a call to multiply by a constant, if the arguments are constant expressions. Like the usual kind of Lisp macro, the compiler macro takes the argument forms as arguments, not the argument values. The special keyword &whole gives the macro access to the entire expression, which is convenient for the unhandled cases, whereby no transformation takes place:

(define-compiler-macro multiply (&whole expr a b)
(if (and (constantp a) (constantp b))
(* (eval a) (eval b))
expr)) ;; no macro recursion if we just return expr; the job is done!

Lisp implementations do not have to honor compiler macros. Usually compilers make use of them, but evaluators do not.

Here is test of the macro using a CLISP interactive session. Note that the multiply function is not actually defined, yet it compiles and executes anyway, which shows that the macro provided the translation something.

$ clisp -q
[1]> (define-compiler-macro multiply (&whole expr a b)
  (if (and (constantp a) (constantp b))
    (* (eval a) (eval b))
    expr))
MULTIPLY
[2]> (defun test1 () (multiply 2 3))
TEST1
[3]> (compile 'test1)
TEST1 ;
NIL ;
NIL
[4]> (disassemble 'test1)

Disassembly of function TEST1
(CONST 0) = 6
[ ... ]
2 byte-code instructions:
0     (CONST 0)                           ; 6
1     (SKIP&RET 1)
NIL
[5]> (test1)
6

[edit] Generic Functions

Lisp's generic functions are part of the object system. Generic functions are compiled to ordinary functions, and so are called in the ordinary way. Internally, however, they have the special behavior of dispatching one or more methods based on specializable parameters.

Methods can be defined right inside the DEFGENERIC construct, but usually are written with separate DEFMETHODS.

Also, the DEFGENERIC is optional, since the first DEFMETHOD will define the generic function, but good practice.

 
;;; terrific example coming
 

[edit] Creative Basic

 
DECLARE Multiply(N1:INT,N2:INT)
 
DEF A,B:INT
 
A=2:B=2
 
OPENCONSOLE
 
PRINT Multiply(A,B)
 
PRINT:PRINT"Press any key to close."
 
DO:UNTIL INKEY$<>""
 
CLOSECONSOLE
 
END
 
SUB Multiply(N1:INT,N2:INT)
 
DEF Product:INT
 
Product=N1*N2
 
RETURN Product
 
'Can also be written with no code in the subroutine and just RETURN N1*N2.
 

[edit] D

// A function:
int multiply1(int a, int b) {
return a * b;
}
 
// Functions like "multiply1" can be evaluated at compile time if
// they are called where a compile-time constant result is asked for:
enum result = multiply1(2, 3); // Evaluated at compile time.
int[multiply1(2, 4)] array; // Evaluated at compile time.
 
// A templated function:
T multiply2(T)(T a, T b) {
return a * b;
}
 
// Compile-time multiplication can also be done using templates:
enum multiply3(int a, int b) = a * b;
 
pragma(msg, multiply3!(2, 3)); // Prints "6" during compilation.
 
void main() {
import std.stdio;
writeln("2 * 3 = ", result);
}

Both the compile-time and run-time output:

6
2 * 3 = 6

[edit] dc

For dc, the functions (called macros) are limited to names from 'a' to 'z' Create a function called 'm'

[*] sm

Use it (lm loads the function in 'm',x executes it, f shows the the stack.)

3 4 lm x f
= 12

[edit] Delphi

function Multiply(a, b: Integer): Integer;
begin
Result := a * b;
end;

[edit] Déjà Vu

multiply a b:
* a b

[edit] DWScript

function Multiply(a, b : Integer) : Integer;
begin
Result := a * b;
end;

[edit] E

def multiply(a, b) {
return a * b
}

(This does not necessarily return a product, but whatever the "multiply" method of a returns. The parameters could be guarded to only accept standard numbers.)

It is also possible to write short anonymous function definitions which do not need explicit returns:

def multiply := fn a, b { a * b }

This definition is identical to the previous except that the function object will not know its own name.

[edit] Efene

multiply = fn (A, B) {
A * B
}
 
@public
run = fn () {
io.format("~p~n", [multiply(2, 5)])
}

[edit] Ela

multiply x y = x * y

Anonymous function:

\x y -> x * y

[edit] Emacs Lisp

(defun multiply (x y)
(* x y))

A "docstring" can be added as follows. This is shown by the Emacs help system and is good for human users. It has no effect on execution.

(defun multiply (x y)
"Return the product of X and Y."
(* x y))

[edit] Erlang

% Implemented by Arjun Sunel
-module(func_definition).
-export([main/0]).
 
main() ->
K=multiply(3,4),
io :format("~p~n",[K]).
 
multiply(A,B) ->
case {A,B} of
{A, B} -> A * B
end.
Output:
12
ok

[edit] Euphoria

function multiply( atom a, atom b )
return a * b
end function

If you declare the arguments as object then sequence comprehension kicks in:

function multiply( object a, object b )
return a * b
end function
 
sequence a = {1,2,3,4}
sequence b = {5,6,7,8}
 
? multiply( 9, 9 )
? multiply( 3.14159, 3.14159 )
? multiply( a, b )
? multiply( a, 7 )
? multiply( 10.39564, b )
Output:
81
9.869587728
{5,12,21,32}
{7,14,21,28}
{51.9782,62.37384,72.76948,83.16512}

[edit] F#

The default will be an integer function but you can specify other types as shown:

let multiply x y = x * y // integer
let fmultiply (x : float) (y : float) = x * y

[edit] Factor

: multiply ( a b -- a*b ) * ;

[edit] Falcon

function sayHiTo( name )
> "Hi ", name
end

[edit] FALSE

[*]     {anonymous function to multiply the top two items on the stack}
m: {binding the function to one of the 26 available symbol names}
2 3m;! {executing the function, yielding 6}

[edit] Fantom

class FunctionDefinition
{
public static Void main ()
{
multiply := |Int a, Int b -> Int| { a * b }
echo ("Multiply 2 and 4: ${multiply(2, 4)}")
}
}

[edit] Fexl

\multiply=(\x\y * x y)

Or if I'm being cheeky:

\multiply=*

[edit] Forth

: fmultiply ( F: a b -- F: c )  F* ;
: multiply ( a b -- c ) * ;

[edit] Fortran

In FORTRAN 66 or later, define a function:

FUNCTION MULTIPLY(X,Y)
REAL MULTIPLY, X, Y
MULTIPLY = X * Y
END

In Fortran 95 or later, define an elemental function, so that this function can be applied to whole arrays as well as to scalar variables:

module elemFunc
contains
elemental function multiply(x, y)
real, intent(in) :: x, y
real :: multiply
multiply = x * y
end function multiply
end module elemFunc
program funcDemo
use elemFunc
 
real :: a = 20.0, b = 30.0, c
real, dimension(5) :: x = (/ 1.0, 2.0, 3.0, 4.0, 5.0 /), y = (/ 32.0, 16.0, 8.0, 4.0, 2.0 /), z
 
c = multiply(a,b) ! works with either function definition above
 
z = multiply(x,y) ! element-wise invocation only works with elemental function
end program funcDemo

It is worth noting that Fortran can call functions (and subroutines) using named arguments; e.g. we can call multiply in the following way:

c = multiply(y=b, x=a)   ! the same as multiply(a, b)
z = multiply(y=x, x=y) ! the same as multiply(y, x)

(Because of commutativity property of the multiplication, the difference between multiply(x,y) and multiply(y,x) is not evident)

Also note that the function result can be declared with a different name within the routine:

module elemFunc
contains
elemental function multiply(x, y) result(z)
real, intent(in) :: x, y
real :: z
z = x * y
end function multiply
end module elemFunc

[edit] Frink

multiply[x,y] := x*y

[edit] GAP

multiply := function(a, b)
return a*b;
end;

[edit] GML

In GML one can not define a function but in Game Maker there is a script resource, which is the equivalent of a function as defined here. Scripts can be exported to or imported from a text file with the following format:

#define multiply
a = argument0
b = argument1
return(a * b)

[edit] Gnuplot

multiply(x,y) = x*y
 
# then for example
print multiply(123,456)

[edit] Go

Function return types in Go are statically typed and never depend on argument types.

The return statement can contain an expression of the function return type:

func multiply(a, b float64) float64 {
return a * b
}

Alternatively, if the return value is named, the return statement does not require an expression:

func multiply(a, b float64) (z float64) {
z = a * b
return
}

[edit] Golfscript

{*}:multiply;

[edit] Groovy

def multiply = { x, y -> x * y }

Test Program:

println "x * y = 20 * 50 = ${multiply 20, 50}"
Output:
x * y = 20 * 50 = 1000

[edit] Haskell

multiply x y = x * y

Alternatively, with help of auto-currying,

multiply = (*)

You can use lambda-function

multiply = \ x y -> x*y

[edit] Haxe

function multiply(x:Float, y:Float):Float{
return x * y;
}

[edit] HicEst

FUNCTION multiply(a, b)
multiply = a * b
END

[edit] Icon and Unicon

procedure multiply(a,b)
return a * b
end

[edit] IDL

The task description is unclear on what to do when the arguments to the function are non-scalar, so here's multiple versions:

function multiply ,a,b
return, a* b
end

If "a" and "b" are scalar, this will return a scalar. If they are arrays of the same dimensions, the result is an array of the same dimensions where each element is the product of the corresponding elements in "a" and "b".

Alternatively, there's this possibility:

function multiply ,a,b
return, product([a, b])
end

This will yield the same result for scalars, but if "a" and "b" are arrays it will return the product of all the elements in both arrays.

Finally, there's this option:

function multiply ,a,b
return, a # b
end

This will return a scalar if given scalars, if given one- or two-dimensional arrays it will return the matrix-product of these arrays. E.g. if given two three-element one-dimensional arrays (i.e. vectors), this will return a 3x3 matrix.

[edit] Inform 6

[ multiply a b;
return a * b;
];

[edit] Inform 7

To decide which number is (A - number) multiplied by (B - number):
decide on A * B.

[edit] Io

multiply := method(a,b,a*b)

[edit] IWBASIC

 
'1. Not Object Oriented Program
 
DECLARE Multiply(N1:INT,N2:INT),INT
 
DEF A,B:INT
 
A=2:B=2
 
OPENCONSOLE
 
PRINT Multiply(A,B)
 
PRINT
 
'When compiled as a console only program, a press any key to continue is automatic.
CLOSECONSOLE
 
END
 
SUB Multiply(N1:INT,N2:INT),INT
 
DEF Product:INT
 
Product=N1*N2
 
RETURN Product
ENDSUB
 
'Can also be written with no code in the subroutine and just RETURN N1*N2.
 
----
 
'2. Not Object Oriented Program Using A Macro
 
$MACRO Multiply (N1,N2) (N1*N2)
 
DEF A,B:INT
 
A=5:B=5
 
OPENCONSOLE
 
PRINT Multiply (A,B)
 
PRINT
 
'When compiled as a console only program, a press any key to continue is automatic.
CLOSECONSOLE
 
END
 
----
 
'3. In An Object Oriented Program
 
CLASS Associate
'functions/methods
DECLARE Associate:'object constructor
DECLARE _Associate:'object destructor
'***Multiply declared***
DECLARE Multiply(UnitsSold:UINT),UINT
'members
DEF m_Price:UINT
DEF m_UnitsSold:UINT
DEF m_SalesTotal:UINT
ENDCLASS
 
DEF Emp:Associate
 
m_UnitsSold=10
 
Ass.Multiply(m_UnitsSold)
 
OPENCONSOLE
 
PRINT"Sales total: ",:PRINT"$"+LTRIM$(STR$(Emp.m_SalesTotal))
 
PRINT
 
CLOSECONSOLE
 
END
 
'm_price is set in constructor
SUB Associate::Multiply(UnitsSold:UINT),UINT
m_SalesTotal=m_Price*UnitsSold
RETURN m_SalesTotal
ENDSUB
 
SUB Associate::Associate()
m_Price=10
ENDSUB
 
SUB Associate::_Associate()
'Nothing to cleanup
ENDSUB
 
 

[edit] J

multiply=: *

Works on conforming arrays of any rank (any number of dimensions, as long as the dimensions of one are a prefix of the dimensions of the other): atoms, lists, tables, etc.

Or, more verbosely (and a bit slower, though the speed difference should be unnoticeable in most contexts):

multiply=: dyad define
x * y
)

Here we use an explicit definition (where the arguments are named) rather than a tacit version (where the arguments are implied). In explicit J verbs, x is the left argument and y is the right argument.

(Note, by the way, that explicit definitions are a subset of tacit definitions -- when the arguments are explicitly named they are still implied in the larger context containing the definition.)

[edit] Java

There are no global functions in Java. The equivalent is to define static methods in a class (here invoked as "Math.multiply(a,b)"). Overloading allows us to define the method for multiple types.

public class Math
{
public static int multiply( int a, int b) { return a*b; }
public static double multiply(double a, double b) { return a*b; }
}

[edit] JavaScript

[edit] ES1-*

Function Declaration

function multiply(a, b) { 
return a*b;
}

[edit] ES3-*

Function Expression

var multiply = function(a, b) {
return a * b;
};

Named Function Expression

var multiply = function multiply(a, b) {
return a * b;
};

Method Definition

var o = {
multiply: function(a, b) {
return a * b;
}
};

[edit] ES5-*

Accessors

var o = {
get foo() {
return 1;
},
set bar(value) {
// do things with value
}
};


[edit] ES6-*

Arrow Function

var multiply = (a, b) => a * b;
var multiply = (a, b) => { return a * b };
 

Concise Body Method Definition

var o = {
multiply(a, b) {
return a * b;
}
};

Generator Functions

function * generator() {
yield 1;
}

[edit] Joy

DEFINE multiply == * .


[edit] jq

Example of a simple function definition:
def multiply(a; b): a*b;
Example of the definition of an inner function:
# 2 | generate(. * .) will generate 2, 4, 16, 256, ...
def generate(f): def r: ., (f | r); r;
The previous example (generate/1) also illustrates that a function argument can be a function or composition of functions. Here is another example:
def summation(f): reduce .[] as $x (0; . + ($x|f));
summation/1 expects an array as its input and takes a function, f, as its argument. For example, if the input array consists of JSON objects with attributes "h" and "w", then to compute SIGMA (h * w) we could simply write:
summation( .h * .w)

[edit] Julia

General function definition

function multiply(a::Number,b::Number)
return a*b
end

Julia also supports "assignment" definition as a shorthand

multiply(a,b) = a*b

In addition, Julia support anonymous functions ("lambda" constructs):

(a,b) -> a*b

[edit] Kaya

program test;
 
// A function definition in Kaya:
Int multiply(Int a, Int b) {
return a * b;
}
 
// And calling a function:
Void main() {
putStrLn(string( multiply(2, 3) ));
}

[edit] Lasso

Lasso supports multiple dispatch — signature definitions determine which method will be invoked.

define multiply(a,b) => {
return #a * #b
}

As this function is so simple it can also be represented like so:

define multiply(a,b) => #a * #b

Using multiple dispatch, different functions will be invoked depending on the functions input.

// Signatures that convert second input to match first input
define multiply(a::integer,b::any) => #a * integer(#b)
define multiply(a::decimal,b::any) => #a * decimal(#b)
 
// Catch all signature
define multiply(a::any,b::any) => decimal(#a) * decimal(#b)

[edit] LFE

 
(defun mutiply (a b)
(* a b))
 

[edit] Liberty BASIC

'     define & call a function
 
print multiply( 3, 1.23456)
 
wait
 
function multiply( m1, m2)
multiply =m1 *m2
end function
 
end

[edit] Locomotive Basic

10 DEF FNmultiply(x,y)=x*y
20 PRINT FNmultiply(2,PI)

Function names are always preceded by "FN" in Locomotive BASIC. Also, PI is predefined by the interpreter as 3.14159265.

[edit]

to multiply :x :y
output :x * :y
end

[edit] LSE64

multiply  : *
multiply. : *. # floating point

[edit] Lua

function multiply( a, b )
return a * b
end

[edit] Lucid

multiply(x,y) = x * y

[edit] M4

define(`multiply',`eval($1*$2)')
 
multiply(2,3)

[edit] Make

In makefile, a function may be defined as a rule, with recursive make used to retrieve the returned value.

A=1
B=1
 
multiply:
@expr $(A) \* $(B)

Invoking it

make -f mul.mk multiply A=100 B=3
> 300

Using gmake, the define syntax is used to define a new function

Works with: gmake
A=1
B=1
 
define multiply
expr $(1) \* $(2)
endef
 
do:
@$(call multiply, $(A), $(B))
 
|gmake -f mul.mk do A=5 B=3

[edit] Mathematica

There are two ways to define a function in Mathematica.

Defining a function as a transformation rule:

multiply[a_,b_]:=a*b

Defining a pure function:

multiply=#1*#2&

[edit] Maxima

f(a, b):= a*b;

[edit] MAXScript

fn multiply a b =
(
a * b
)

[edit] Mercury

% Module ceremony elided...
:- func multiply(integer, integer) = integer.
multiply(A, B) = A * B.

[edit] Metafont

Metafont has macros, rather than functions; through those the language can be expanded. According to the kind of macro we are going to define, Metafont has different ways of doing it. The one suitable for this task is called primarydef.

primarydef a mult b = a * b enddef;
t := 3 mult 5; show t; end

The primarydef allows to build binary operators with the same priority as *. For a more generic macro, we can use instead

def mult(expr a, b) = (a * b) enddef;
t := mult(2,3);
show t;
end

[edit] МК-61/52

ИП0 ИП1 * В/О

Function (subprogram) that multiplies two numbers. Parameters in registers Р0 and Р1, the result (return value) in register X. Commands ИП0 and ИП1 cause the contents of the corresponding registers in the stack, the more they multiplied (command *) and then code execution goes to the address from which the call subprogram (command В/О).

[edit] Modula-2

PROCEDURE Multiply(a, b: INTEGER): INTEGER;
BEGIN
RETURN a * b
END Multiply;

[edit] Modula-3

PROCEDURE Multiply(a, b: INTEGER): INTEGER =
BEGIN
RETURN a * b;
END Multiply;

[edit] MUMPS

MULTIPLY(A,B);Returns the product of A and B
QUIT A*B

[edit] Neko

// a function definition can be written either as
var multiply = function(a, b) {
a * b
}
 
// or
function multiply(a, b) {
a * b
}
 
// and calling a function
$print(multiply(2,3));

Output: 6

[edit] Nemerle

public Multiply (a : int, b : int) : int  // this is either a class or module method
{
def multiply(a, b) { return a * b } // this is a local function, can take advantage of type inference
return multiply(a, b)
}

[edit] NetRexx

/* NetRexx */
options replace format comments java crossref savelog symbols binary
 
pi = 3.14159265358979323846264338327950
radiusY = 10
in2ft = 12
ft2yds = 3
in2mm = 25.4
mm2m = 1 / 1000
radiusM = multiply(multiply(radiusY, multiply(multiply(ft2yds, in2ft), in2mm)), mm2m)
 
say "Area of a circle" radiusY "yds radius: " multiply(multiply(radiusY, radiusY), pi).format(3, 3) "sq. yds"
say radiusY "yds =" radiusM.format(3, 3) "metres"
say "Area of a circle" radiusM.format(3, 3)"m radius:" multiply(multiply(radiusM, radiusM), pi).format(3, 3)"m**2"
 
 
/**
* Multiplication function
*/

method multiply(multiplicand, multiplier) public static returns Rexx
 
product = multiplicand * multiplier
return product
Output:
Area of a circle 10 yds radius:  314.159 sq. yds
10 yds =   9.144 metres
Area of a circle   9.144m radius: 262.677m**2

[edit] NewLISP

> (define (my-multiply a b) (* a b))
(lambda (a b) (* a b))
> (my-multiply 2 3)
6

[edit] Nial

Using variables

multiply is operation a b {a * b}

Using it

|multiply 2 3
=6

Point free form

mul is *

Using it

|mul 3 4
=12

Nial also allows creation of operators

multiply is op a b {a * b}

Using it.

|2 multiply 3
=6
|multiply 2 3
=6

Since this is an array programming language, any parameters can be arrays too

|mul 3 [1,2]
=3 6
|mul [1,2] [10,20]
=10 40

[edit] Nimrod

Nimrod has a magic variable, `result`, which can be used as a substitute for `return`. The `result` variable will be returned implicitly.

proc multiply(a, b: Int): Int =
result = a * b

Here is the same function but with the use of the `return` keyword.

proc multiply(a, b: Int): Int =
return a * b

[edit] Oberon-2

Oberon-2 uses procedures, and has a special procedure called a "Function Procedure" used to return a value.

PROCEDURE Multiply(a, b: INTEGER): INTEGER;
BEGIN
RETURN a * b;
END Multiply;

[edit] Objeck

function : Multiply(a : Float, b : Float) ~, Float {
return a * b;
}

[edit] OCaml

let int_multiply x y = x * y
let float_multiply x y = x *. y

[edit] Octave

function r = mult(a, b)
r = a .* b;
endfunction

[edit] OOC

 
multiply: func (a: Double, b: Double) -> Double {
a * b
}
 

[edit] ooRexx

[edit] Internal Procedure

 
SAY multiply(5, 6)
EXIT
 
multiply:
PROCEDURE
PARSE ARG x, y
RETURN x*y

[edit] ::Routine Directive

 
say multiply(5, 6)
 
::routine multiply
use arg x, y
return x *y
 

[edit] OpenEdge/Progress

FUNCTION multiply RETURNS DEC (a AS DEC , b AS DEC ):
RETURN a * b .
END.

[edit] Oz

fun {Multiply X Y}
X * Y
end

Or by exploiting first-class functions:

Multiply = Number.'*'

[edit] PARI/GP

multiply(a,b)=a*b;

or

multiply=(a,b)->a*b;

Note that in both cases the ; is part of the definition of the function, not of the function itself: it suppresses the output of the function body, but does not suppress the output of the function when called. To do that, either double the semicolon (which will suppress the output of both) or wrap in braces:

multiply={(a,b)->a*b;}

which will return a function which calculates but does not return the product.

[edit] Pascal

(all versions and dialects)

function multiply(a,b: real): real;
begin
multiply := a*b;
end;

[edit] Perl

The most basic form:

sub multiply { return $_[0] * $_[1] }

or simply:

sub multiply { $_[0] * $_[1] }

Arguments in Perl subroutines are passed in the @_ array, and they can be accessed directly, first one as $_[0], second one as $_[1], etc. When the above function is called with only one or no arguments then the missing ones have an undefined value which is converted to 0 in multiplication.

This is an example using subroutine prototypes:

sub multiply( $$ )
{
my ($a, $b) = @_;
return $a * $b;
}

The above subroutine can only be called with exactly two scalar values (two dollar signs in the signature) but those values may be not numbers or not even defined. The @_ array is unpacked into $a and $b lexical variables, which are used later.

The arguments can be automatically unpacked into lexical variables using the experimental signatures feature (in core as of 5.20):

use experimental 'signatures';
sub multiply ($x, $y) {
return $x * $y;
}

[edit] Perl 6

Without a signature:

sub multiply { return @_[0] * @_[1]; }

The return is optional on the final statement, since the last expression would return its value anyway. The final semicolon in a block is also optional. (Beware that a subroutine without an explicit signature, like this one, magically becomes variadic (rather than nullary) only if @_ or %_ appear in the body.) In fact, we can define the variadic version explicitly, which still works for two arguments:

sub multiply { [*] @_ }

With formal parameters and a return type:

sub multiply (Rat $a, Rat $b --> Rat) { $a * $b }

Same thing:

sub multiply (Rat $a, Rat $b) returns Rat { $a * $b }
my Rat sub multiply (Rat $a, Rat $b) { $a * $b }

It is possible to define a function in "lambda" notation and then bind that into a scope, in which case it works like any function:

my &multiply := -> $a, $b { $a * $b };

Another way to write a lambda is with internal placeholder parameters:

my &multiply := { $^a * $^b };

(And, in fact, our original @_ above is just a variadic self-declaring placeholder argument. And the famous Perl "topic", $_, is just a self-declared parameter to a unary block.)

You may also curry both built-in and user-defined operators by supplying a * (known as "whatever") in place of the argument that is not to be curried:

my &multiply := * * *;

This is not terribly readable in this case due to the visual confusion between the whatever star and the multiplication operator, but Perl knows when it's expecting terms instead of infixes, so only the middle star is multiplication. It tends to work out much better with other operators. In particular, you may curry a cascade of methods with only the original invocant missing:

@list.grep( *.substr(0,1).lc.match(/<[0..9 a..f]>/) )

This is equivalent to:

@list.grep( -> $obj { $obj.substr(0,1).lc.match(/<[0..9 a..f]>/) )

[edit] PHL

@Integer multiply(@Integer a, @Integer b) [
return a * b;
]

[edit] PHP

function multiply( $a, $b )
{
return $a * $b;
}

[edit] PicoLisp

(de multiply (A B)
(* A B) )

[edit] Pike

int multiply(int a, int b){
return a * b;
}

[edit] PL/I

PRODUCT: procedure (a, b) returns (float);
declare (a, b) float;
return (a*b);
end PRODUCT;

[edit] PL/SQL

FUNCTION multiply(p_arg1 NUMBER, p_arg2 NUMBER) RETURN NUMBER 
IS
v_product NUMBER;
BEGIN
v_product := p_arg1 * p_arg2;
RETURN v_product;
END;

[edit] Pop11

define multiply(a, b);
a * b
enddefine;

[edit] PostScript

Inbuilt:

3 4 mul

Function would be:

/multiply{
/x exch def
/y exch def
x y mul =
}def

[edit] PowerShell

The most basic variant of function definition would be the kind which uses positional parameters and therefore doesn't need to declare much:

function multiply {
return $args[0] * $args[1]
}

Also, the return statement can be omitted in many cases in PowerShell, since every value that "drops" out of a function can be used as a "return value":

function multiply {
$args[0] * $args[1]
}

Furthermore, the function arguments can be stated and named explicitly:

function multiply ($a, $b) {
return $a * $b
}

There is also an alternative style for declaring parameters. The choice is mostly a matter of personal preference:

function multiply {
param ($a, $b)
return $a * $b
}

And the arguments can have an explicit type:

function multiply ([int] $a, [int] $b) {
return $a * $b
}

[edit] Prolog

Prolog, as a logic programming languages, does not have user-supplied functions available. It has only predicates; statements which are "true" or "false". In cases where values have to be "returned" a parameter is passed in that is unified with the result. In the following predicate the parameter "P" (for "Product") is used in this role. The following code will work in any normal Prolog environment (but not in things like Turbo Prolog or Visual Prolog or their ilk):

multiply(A, B, P) :- P is A * B.

This is what it looks like in use:

go :-
multiply(5, 2, P),
format("The product is ~d.~n", [P]).

This can be a little bit jarring for those used to languages with implicit return values, but it has its advantages. For example unit testing of such a predicate doesn't require special frameworks to wrap the code:

test_multiply :-
multiply(5, 2, 10), % this will pass
multiply(3, 4, 11). % this will not pass

Still, the lack of user-defined functions remains an annoyance.

Prolog, however, is a remarkably malleable language and through its term re-writing capabilities the function-style approach could be emulated. The following code relies on the function_expansion pack (separately installed through the packs system) for SWI-Prolog. Similar code could be made in any Prolog implementation, however.

:- use_module(library(function_expansion)).
 
user:function_expansion(multiply(A, B), P, P is A * B). % "function" definition
 
go :-
format("The product is ~d.~n", [multiply(5, 2)]).

While the function definition is perhaps a bit more involved, the function use is now pretty much the same as any other language people are used to. The "magic" is accomplished by the compiler rewriting the go/0 term into the following code:

go :-
A is 5*2,
format('The product is ~d.~n', [A]).

[edit] PureBasic

Procedure multiply(a,b)
ProcedureReturn a*b
EndProcedure

[edit] Python

Function definition:

def multiply(a, b):
return a * b

Lambda function definition:

multiply = lambda a, b: a * b

A callable class definition allows functions and classes to use the same interface:

class Multiply:
def __init__(self):
pass
def __call__(self, a, b):
return a * b
 
multiply = Multiply()
print multiply(2, 4) # prints 8

(No extra functionality is shown in this class definition).

[edit] Q

multiply:{[a;b] a*b}

or

multiply:{x*y}

or

multiply:*

Using it

multiply[2;3]
6

[edit] R

mult <- function(a,b) a*b

In general:

mult <- function(a,b) {
a*b
# or:
# return(a*b)
}

[edit] Racket

A simple function definition that takes 2 arguments.

 
(define (mutiply a b)
(* a b))
 

Using an explicit lambda is completely equivalent:

 
(define multiply (lambda (a b) (* a b)))
 

[edit] Raven

define multiply use a, b
a b *

Or optional infix:

define multiply use a, b
(a * b)

Or skip named vars:

define multiply *

[edit] REALbasic

 
Function Multiply(a As Integer, b As Integer) As Integer
Return a * b
End Function
 

[edit] REBOL

REBOL actually already has a function called 'multiply', which is a native compiled function. However, since it's not protected, I can easily override it:

multiply: func [a b][a * b]

[edit] Retro

: multiply ( nn-n ) * ;

[edit] REXX

[edit] version 1

multiply: return arg(1) * arg(2)    /*return the product of the two arguments.*/

[edit] version 2

Because REXX will return the same precision as the multiplicands, we can do some beautification with the resultant product.

I.E.:             3.0 * 4.00     yields the product:     12.000

This version eliminates the   .000   from the product.

multiply: return arg(1) * arg(2) / 1    /*return with a normalized product of 2 args. */

[edit] RLaB

In RLaB the functions can be built-in (compiled within RLaB, or part of the shared object library that is loaded per request of user), or user (written in RLaB script). Consider an example:

>> class(sin)
function
>> type(sin)
builtin

Functions are a data class on their own, or they can be member of a list (associative array).

1. user function specified from built-in functions, here basic addition

f = function(x, y)
{
return x + y;
};
 
>> class(f)
function
>> type(f)
user

2. function can be member of a list (associative array)

somelist = <<>>;
somelist.f = function(x, y)
{
rval = x + y;
return rval;
};

3. user function which uses a function that is specified as a member of some list, here we use somelist from above:

g = function(x, y)
{
global(somelist);
rval = x * somelist.f(x, 2*y);
return rval;
};

[edit] Ruby

def multiply(a, b)
a * b
end

[edit] Sather

class MAIN is
-- we cannot have "functions" (methods) outside classes
mult(a, b:FLT):FLT is return a*b; end;
 
main is
#OUT + mult(5.2, 3.4) + "\n";
end;
end;

[edit] Scala

def multiply(a: Int, b: Int) = a * b

[edit] Scheme

(define multiply *)

Alternately,

(define (multiply a b)
(* a b))

[edit] Seed7

const func float: multiply (in float: a, in float: b) is
return a * b;

[edit] Slate

define: #multiply -> [| :a :b | a * b].

or using a macro:

define: #multiply -> #* `er.

The block may also be installed as a method like so:

a@(Number traits) multiplyBy: b@(Number traits) [a * b].

or more explicitly (without sugar):

[| :a :b | a * b] asMethod: #multipleBy: on: {Number traits. Number traits}.

[edit] Smalltalk

|mul|
mul := [ :a :b | a * b ].

[edit] SNOBOL4

          define('multiply(a,b)') :(mul_end)
multiply multiply = a * b  :(return)
mul_end
* Test
output = multiply(10.1,12.2)
output = multiply(10,12)
end
Output:
   123.22
   120

[edit] SNUSP

For expediency, the function is adding three values, instead of multiplying two values. Another function, atoi (+48) is called before printing the result.

+1>++2=@\=>+++3=@\==@\=.=#  prints '6'
| | \=itoa=@@@+@+++++#
\=======!\==!/===?\<#
\>+<-/

[edit] SPARK

The function definition (multiplies two standard Integer):

package Functions is
function Multiply (A, B : Integer) return Integer;
--# pre A * B in Integer; -- See note below
--# return A * B; -- Implies commutativity on Multiply arguments
end Functions;

Note: how do you ensure then “A * B in Integer” ? Either with a proof prior to Multiply invokation or using another form of Multiply where input A and B would be restricted to a range which ensures the resulting product is always valid. Exemple :

type Input_Type is range 0 .. 10;
type Result_Type is range 0 .. 100;

and had a version of Multiply using these types. On the other hand, if arguments of Multiply are constants, this is provable straight away.

The Multiply's implementation:

package body Functions is
function Multiply (A, B : Integer) return Integer is
begin
return A * B;
end Multiply;
end Functions;

[edit] Standard ML

val multiply = op *

Equivalently,

fun multiply (x, y) = x * y

Curried form:

fun multiply x y = x * y

[edit] Swift

func multiply(a: Double, b: Double) -> Double {
return a * b
}

[edit] Tcl

Strictly as described in the task:

proc multiply { arg1 arg2 } {
return [expr {$arg1 * $arg2}]
}
Works with: Tcl version 8.5

You can also create functions that work directly inside expressions. This is done by creating the command with the correct name (that is, in the tcl::mathfunc namespace):

proc tcl::mathfunc::multiply {arg1 arg2} {
return [expr {$arg1 * $arg2}]
}
 
# Demonstrating...
if {multiply(6, 9) == 42} {
puts "Welcome, Citizens of Golgafrincham from the B-Ark!"
}

[edit] TI-89 BASIC

multiply(a, b)
Func
Return a * b
EndFunc

[edit] Toka

[ ( ab-c ) * ] is multiply

[edit] TXR

In TXR, there are pattern functions which are predicates that perform pattern matching and variable capture. A call to this type of function call can specify unbound variables. If the function succeeds, it can establish bindings for those variables.

Here is how to make a pattern function that multiplies, and call it. To multiply the numbers, we break out of the pattern language and invoke Lisp evaluation: @(* a b)

@(define multiply (a b out))
@(bind out @(* a b))
@(end)
@(multiply 3 4 result)
$ txr -B multiply.txr
result="12"

In the embedded Lisp dialect, it is possible to write an ordinary function that returns a value:

@(do (defun mult (a b) (* a b))
(put-line `3 * 4 = @(mult 3 4)`))
$ txr multiply2.txr
3 * 4 = 12

[edit] UNIX Shell

Note that in the Unix shell, function definitions do not include any argument specifications within the parentheses. Instead arguments to functions are obtained using the positional parameters.

Works with: Bourne Shell
multiply() {
# There is never anything between the parentheses after the function name
# Arguments are obtained using the positional parameters $1, and $2
# The return is given as a parameter to the return command
return `expr "$1" \* "$2"` # The backslash is required to suppress interpolation
}
 
# Call the function
multiply 3 4 # The function is invoked in statement context
echo $? # The dollarhook special variable gives the return value
Works with: Bash

return an exit code

multiply() {
return $(($1 * $2))
}
 
multiply 5 6
echo $?

echo the result

multiply() {
echo -n $(($1 * $2))
}
 
echo $(multiply 5 6)

[edit] Ursala

Functions are declared with an equals sign like constants of any other type. They may be specified by lambda abstraction, with dummy variables in double quotes, or in point-free form, or any combination. The way multiplication is defined depends on the type of numbers being multiplied. For this example, numbers in standard IEEE double precision are assumed, and the multiply function is defined in terms of the system library function, called using the syntax math..mul. This is the definition in point free form,

multiply = math..mul

this is the definition using lambda abstraction

multiply = ("a","b"). math..mul ("a","b")

and this is the definition using pattern matching.

multiply("a","b") = math..mul ("a","b")

[edit] V

V uses stack for input arguments and '.' is a word that takes a quote and binds the first word to the sequence of actions supplied in the quote.

[multiply *].

Using it

2 3 multiply
=6

V also allows internal bindings.

[multiply
[a b] let
a b *].

[edit] VBScript

function multiply( multiplicand, multiplier )
multiply = multiplicand * multiplier
end function

Usage:

dim twosquared
twosquared = multiply(2, 2)

[edit] Visual Basic .NET

Function Multiply(ByVal a As Integer, ByVal b As Integer) As Integer
Return a * b
End Function

Call the function

Multiply(1, 1)

[edit] Wart

A straightforward way to say how calls of the form (multiply a b) are translated:

def (multiply a b)
a*b
(multiply 3 4)
=> 12

Functions can also use keyword args.

(multiply 3 :a 4)  # arg order doesn't matter here, but try subtract instead
=> 12

Finally, we can give params better keyword args using aliases:

def (multiply a b|by)
(* a b)
multiply 3 :by 4
=> 12

[edit] X86 Assembly

X86 Assembly doesn't really have functions. Instead, it has labels that are called. Function arguments can be pushed onto the stack prior to calling or passed to the function in registers. The system will usually have some sort of calling conventions to facilitate inter-operation between languages.

[edit] Unix

Function definition and calling conventions on a Unix-like system are specified in the book "System V Application Binary Interface: Intel 386 Architecture Processor Supplement". These are the conventions used by the C language and also most other languages.

The stack, for two 32-bit integer parameters, is

  • [esp+8] second parameter
  • [esp+4] first parameter
  • [esp] return address

The return value is left in the eax register. ecx and edx are "scratch" registers meaning the called routine doesn't need to preserve their values. (In the code below edx is clobbered.)

The following is Unix-style "as" assembler syntax (including GNU as). The resulting function can be called from C with multiply(123,456).

        .text
.globl multiply
.type multiply,@function
multiply:
movl 4(%esp), %eax
mull 8(%esp)
ret

The .type directive is important for code which will go into a shared library. You can get away without it for a static link. It ensures the linker knows to dispatch calls from the mainline to the function via a PLT entry. (If omitted the code is copied at runtime into some mainline space. Without a .size directive only 4 bytes will be copied.)

[edit] NASM

Works with: NASM
section .text
global _start
 
_multiply_regs:
mul ebx
mov eax, ebx
ret
 
_multiply_stack:
enter 2,0
mov eax, [esp+4]
mov ebx, [esp+8]
mul ebx
mov eax, ebx
leave
ret
 
_start:
mov ax, 6 ;The number to multiply by
mov ebx, 16 ;base number to multiply.
call _multiply_regs
push 6
push 16
call _multiply_stack

[edit] MASM

However, in MASM we do have function statements due to the preprocessor.

Works with: MASM
multiply proc arg1:dword, arg2:dword
mov eax, arg1
mov ebx, arg2
mul ebx
mov eax, ebx
ret
multiply endp

Then to call it.

invoke multiply, 6, 16
;or..
push 16
push 6
call multiply

Return values are usually put into the register EAX. This, of course is not a must it's simply that it's somewhat of a unofficial standard. For example, C/C++ preprocessors/compilers will translate "return value" into "mov eax, value" followed by the return to caller instruction "ret".

[edit] XPL0

func Multiply(A, B);    \the characters in parentheses are only a comment
int A, B; \the arguments are actually declared here, as integers
return A*B; \the default (undeclared) function type is integer
\no need to enclose a single statement in brackets
 
func real FloatMul(A, B); \floating point version
real A, B; \arguments are declared here as floating point (doubles)
return A*B;

[edit] XSLT

Templates are the closest things XSLT has to user defined functions. They can be declared to be called by name and/or to be applied to all nodes in a matching set and given "mode". Both types of template can take named parameters with default values. Templates also have a "context" node used as the base of XPath expressions (kind of like an implied "this" of an object's method).

<xsl:template name="product">
<xsl:param name="a" select="2"/>
<xsl:param name="b" select="3"/>
<fo:block>product = <xsl:value-of select="$a * $b"/></fo:block>
</xsl:template>
 
<xsl:call-template name="product">
<xsl:with-param name="a">4</xsl:with-param>
<xsl:with-param name="b">5</xsl:with-param>
</xsl:call-template>

<xsl:call-template name="product"/> <-- using default parameters of 2 and 3 -->

[edit] Yorick

func multiply(x, y) {
return x * y;
}

Example of interactive usage:

> multiply(2, 4.5)
9

[edit] zkl

fcn multiply(x,y){x*y}
fcn(x,y){x*y}(4.5,3) // --> 13.5
Since all functions are vararg:
fcn multiply{vm.arglist.reduce('*)}
multiply(1,2,3,4,5) //--> 120
Operators are first class objects so:
var mul=Op("*"); mul(4,5) //-->20

[edit] ZX Spectrum Basic

On the ZX Spectrum, function names are limited to one letter. Note that the function becomes effective as soon as it is entered into the program, and does not need to be run

10 PRINT FN m(3,4): REM call our function to produce a value of 12
20 STOP
9950 DEF FN m(a,b)=a*b
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