• PHP

function square(int $x): int
{
    return $x * $x;
}

// square(4) -> 16
// square(3.4) -> Uncaught TypeError: Argument 1 passed to square() must be of the type int, float given

• Ada

function Square (X : Integer) return Integer is
begin
   return X * X;
end Square;

• C

int square(int x){
  return x*x;
}

• Caml

let square x = x*x

• Clojure

(defn square [x]
  (* x x))

• C++

int square(int x){
  return x*x;
}

• C#

void Square(ref int x)
{
    x = x * x;
}

• C#

double Square(int value) => System.Math.Pow(value, 2);

• C#

int Square(int x) => (int)Math.Pow(x, 2);

• C#

int Square(int x)
{
    return x * x;
}

• D

alias fun = (in a){return a * a;};

• D

int square(int x) {
   return x*x;
}

• Dart

int square(int x) => x * x;

• Elixir

@spec square(integer) :: integer
def square(x) when is_integer(x), do: x*x

• Erlang

-spec square(integer()) -> integer().
square(X) when is_integer(X) -> X * X.

• Fortran

module foo
  implicit none
contains
  function square(i) result(res)
    integer, intent(in) :: i
    integer :: res
    res = i * i
  end function square
end module foo

• Go

func square(x int) int {
  return x*x
}

• Groovy

int square(int x){
  return x*x
}

• Haskell

square x = x * x

• Haskell

square x = x^2

• Haskell

square x = x**2

• JS

const square = (x) => x * x;

• JS

function square(x) { 
	return x * x;
}

• JS

const square = (number) => Math.pow(number, 2);

• JS

const square = n => n**2

• Java

Function<Integer,Integer> squareFunction = x -> x * x;

• Java

BigInteger square(BigInteger a) {
    return a.multiply(a);
}

• Java

interface F { int get(int a); }
F square = x -> x * x;

• Java

int square(int a) { return (int) pow(a, 2); }

• Java

int square(int x){
  return x*x;
}

• Java

int square(int a) { return a * a; }

• Kotlin

fun square(x: Int) = x * x

• Lisp

(defun square (x)
  (* x x))

• Lua

function square(x)
	return x*x
end

• Obj-C

int square(int x) {
  return x*x;
}

• Pascal

Function square(x: Integer): Integer;
Begin
  Result := x*x;
End;

• Perl

sub square {
    my ($i) = @_;
    return $i ** 2;
}

• Python

square = lambda x: x * x

• Python

def square(x):
    return x**2

• Python

def square(x):
    return x*x

• Ruby

def square(x)
  x*x
end

• Ruby

def square(x) = x*x

• Rust

fn square(x : u32) -> u32 { x * x }

• Scala

def square(x:Int): Int = x*x

• Scheme

(define square
    (lambda (x)
        (* x x)))

• Scheme

(define (square x)
    (* x x))

• Smalltalk

[:anInteger | anInteger squared]

• VB

Function Square(x As Integer) As Integer
    Return x * x
End Function

• VB

Function Square(x As Integer) As Double
    Return x ^ 2
End Function