From: Edward Faulkner <ef@...>
Date: 2005-10-03T13:32:46+09:00
Subject: Re: Functional Programming? (was Re: Lazy evaluaton)

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On Sun, Oct 02, 2005 at 05:16:45AM +0900, Jay Levitt wrote:
> From reading this thread, I would have assumed that FP is another
> word for "procedural" but clearly it's much, much more.

Indeed, functional programming is almost the *opposite* of procedural.
In a procedural program, most lines are executed for their side
effects.  In a functional program, most lines are executed for their
value.

The key idea in functional programming is that the functions you
define are functions in the mathematical sense.  If you call one twice
with the same arguments, you'll always get the same answer each time.
They have no internal state and no side effects.

In practice most programs need non-functional parts too, but you can
keep those isolated.

By keeping your code functional, you make it easier to test and debug.
It's inherently thread safe, and optimizations like lazy evaluation
and memoization can be introduced transparently by the
compiler/interpreter.

regards,
Ed

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