From: John Carter <john.carter@...>
Date: 2005-10-20T06:07:19+09:00
Subject: Re: Functional with Ruby

On Thu, 20 Oct 2005, Andreas Semt wrote:

> Which is the best way to say it in Ruby (functional style)?

I'm not going to answer your concrete question. I'm going to answer the 
question you should be asking....

The answer is with the exception of the the non '!' string methods and 
numbers most of ruby operations are non-"functional pure" in the sense 
that they have side effects and change state.

Thus to recapture "functional" programming purity in Ruby, for most 
objects and operations on them requires you to make very heavy use of 
the clone method. ie. Force yourself to go obj.clone.operation to make 
ruby into something like the "Self" language.

Certainly in some contexts (eg. when you can prove there are no other 
references to the object in question) a clone + modify is equivalent to 
just a modify. Thus you can make an optimization in such cases, but you 
will receive very little support from the language in proving this.

It doesn't even have C++'s "const" keyword. Although it does have 
"freeze", which unfortunately only works at run time after the object has 
been frozen, which tends to be a bit late.

On the other hand ruby is a "functional" language in the sense that procs, 
blocks and methods, etc are all first order objects and you can curry dice 
and slice them. It even has several flavours of eval.


John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
New Zealand

Carter's Clarification of Murphy's Law.

"Things only ever go right so that they may go more spectacularly wrong later."

From this principle, all of life and physics may be deduced.