A function can be a pure function, provided it should not have any external variable which will alter the behaviour of that variable.

In object oriented programming language, an interface is a description of all functions that a class must have in order to be a new interface.

An object is an instance created from the class. The interface defines an object's visibility to the outside world.

A class declaration combines the external interface with an implementation of that interface.

The definition is introduced by the keyword let rec, followed by the name of the function and its arguments.
Syntax:
let rec final a2....an: = K

The definition is introduced by the keyword let, followed by the name of the function and its arguments.
Syntax:
let odd x:=

The two types of function specification are
(i) Parameter without type.
(ii) parameter with type.

Definitions bind values to names. Definitions are distinct syntactic blocks. Definitions can have expressions nested inside them and vice-versa.

let rec monochromatize a b c :=
if a > 0 then
a, b, c:= a-1, b-1, c+2
else
a:=0, b:=0, c:= a + b + c
return c

let y: = 0
(int) inc (int) x
y: =y+x;
return (y)

let square x
return: x * x
let i: = 0;
ifi < strlen> (s) then
-- Do something which doesn't affect s
++i

A function definition which call itself is called recursive function.

(requires: b > 0 )
(returns: a to the power of b)
let rec pow (a: int) (b: int) : int :=
if (b=0) then 1
else a * pow b (a-1 )

(requires: b>=0 )
(returns: a to the power of b)
let rec pow a b:=
if b=0 then I
else a * pow a (b-1)

Parameters are the variables in a function definition and arguments are the values which are passed to a function definition.