From: Mathieu Bouchard <matju@...>
Date: 2005-02-04T18:26:38+09:00
Subject: Re: [Terminology] What's the Ruby/OO name for this paradigm?


On Thu, 3 Feb 2005, E S wrote:
> In my current project, one of the main paradigms is code such as in 
> the following example. I'm wondering if there's a Ruby/OO designation 
> for it so that I wouldn't have to always show some excerpt when 
> describing the project. It's sort of an inverse continuation passing 
> scheme (which, in itself, isn't exactly a prime OO term). 
> 
> Anything? Input on the style welcome, too, by the way: is this hard to
> understand/unintuitive/there's a better way/etc.?

It is called "delayed evaluation". The pattern is that instead of having a
value of type A, you have a function taking no arguments whose return is
of type A. Some take this concept further, ensuring the function is only
actually called once, and the result is cached (Scheme has a macro called
DELAY for that). That's the kind of thing you'd do to have lazy semantics
in a non-lazy language.

Don't listen to those who might call this "currying". Currying means
decomposing the argument list like this:

  f = lambda{|a,b,c| a*b+c }
  p f[4,10,2]

  g = lambda{|a| lambda{|b| lambda{|c| a*b+c }}}
  p g[4][10][2]

here g is called the currying of f.

typewise, that's (A*B*C)->D becoming A->(B->(C->D)).

_____________________________________________________________________
Mathieu Bouchard -=- Montr�al QC Canada -=- http://artengine.ca/matju