From: Robert Klemme <shortcutter@...>
Date: 2008-01-30T07:30:18+09:00
Subject: Re: neat idea from arc

On 29.01.2008 23:07, Martin DeMello wrote:
> Paul Graham just released Arc (http://paulgraham.com/arc0.html), a
> lisp dialect with an emphasis on "quick-and-dirty" exploratory
> programming, and compactness of code. One of the ideas he threw in
> seems like it might fit well into Ruby too - when filtering functions
> like keep and rem (select and reject) are given a value rather than a
> function, they implicitly construct the equality function and pass
> that in instead. The ruby equivalent would be to have select, reject,
> partition, any? and all? (and possibly some others I'm overlooking) do
> the following:
> 
> def select(arg, &blk)
>   if block_given?
>     old_select(&blk)
>   else
>     old_select {|x| arg === x}
>   end
> end

You either need "*arg" or "arg = nil" because otherwise the method 
cannot be invoked without arg.  Here's another way to write it:

module Enumerable
   def select2(a = nil, &b)
     select(&(b || lambda {|e| a === e}))
   end
end

but I guess your variant is more efficient.

> and likewise for the others
> 
> So we can write, for instance
> 
> ints = input.select Integer
> 
> lcase = words.reject /[A-Z]/
> 
> and so on. What say you?

Sounds good!  Btw, there is already #grep which works like the new 
#select with argument but I agree, the idea to put this in one method 
sounds better.

Kind regards

	robert