From: ser@... (Sean Russell)
Date: 2004-07-07T00:17:44+09:00
Subject: Re: Functional Ruby (Re: Why I don't use Ruby.)

James Britt <jamesUNDERBARb@neurogami.com> wrote in message news:<40E586A6.9040301@neurogami.com>...
> Um, I don't see this as true.  Certainly one can write all the 
> procedural  code one likes in Ruby (I know *I've* managed to do it), and 
> I believe the same is pretty much true for writing functional code.

"Functional code" is a rather broad term, but one popular feature of
many functional languages is pattern matching[1], which Ruby doesn't
support.  Indeed, the entire structure of functional programs is
generally alien enough to OO or procedural languages that any mapping
you could do would be difficult to describe as being functional,
except in the broadest sense.

Procedural and OO languages are very similar.  Functional languages
require a different mindset, and I believe that it *is* a stretch to
claim that you can do functional programming in Ruby.  Furthermore,
I'd say it would be difficult to do pure procedural programming in
Ruby -- you'd have to redefine most of the API to avoid calling
methods on objects -- however, it could be done.


[1] in the sense of matching the appropriate function based on the
arguments.
Consider the function sum().  Given a recursive procedural definition:

int sum( array ) {
  if ( length( array ) == 0)
    return 0;
  else
    return array[0] + sum( subset( array, 1, length( array ) - 1 ) );
}

In Ruby(procedural) this might be:

sum( array ) {
  return 0 if length( array ) == 0
  return array[0] + sum( subset( array, 1, -1 ) )
}

(being pedantic, and avoiding *all* OO methods).  In Haskell, this
code would be:

func []    = 0
func (x:y) = x + func( y )

Converting the Haskell code to Ruby would give you the same code as
the procedural version (again, if you avoid all of the OO
constructions that you possibly can).  I don't think I'd be
exaggerating if I said that, in general, Ruby( procedural ) == Ruby(
functional ), and yet, functonal and procedural programming are
fundamentally different styles.

--- SER