CSC/ECE 517 Fall 2010/ch1 1e bb

Functional Programming

Functional programming treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes on the application of functions, also called applicative programming. Functional programming decomposes a problem into a set of functions. Ideally, functions only take inputs and produce outputs, and don't have any internal state that affects the output produced for a given input. Well-known functional languages include the ML family (Standard ML, OCaml, and other variants) and Haskell. In a functional program, input flows through a set of functions. Each function operates on its input and produces some output A more practical benefit of functional programming is that it forces you to break apart your problem into small pieces. Small functions are also easier to read and to check for errors, thus debugging is easier. Functional Programming discourages the use of variables.

 fun factorial (0 : int) : int = 1
 | factorial (n : int) : int = n * factorial (n-1)

The above code snippet is a functional code written in ML to compute factorial of an integer recursively. In the first line, the fun factorial keyword defines a function. The notation (0: int) can be read as ‘0 is of type int’ and : int =1 means that the default return value is 1 when 0 is passed as an argument.

In the second line, (n: int) sets the argument n to integer. int = n * factorial (n-1) means the return value of recursive computation is an integer.

We can observe here that no additional variables are used here, no state information is maintained and there are no side-effects to any variables.