On Wed, May 27, 2009 at 02:21:40PM -0400, Mark J. Reed wrote:
> On Wed, May 27, 2009 at 1:59 PM, Daniel Carrera <
> daniel.carr...@theingots.org> wrote:
> > Wow... That's a foldl! In a functional language, that would be called a
> > fold.
>
> In Haskell it may be called fold (well, foldl and foldr), but the concept
> has has a variety of names. Two of the more common ones are "reduce" and
> "inject"; I believe Perl6 chose "reduce" for consistency with the Perl5
> List::Util module. Common Lisp and Python also call it "reduce":
>
> (defun ! (n)
> (reduce #'* (loop for i from 1 to n collecting i)))
>
>
> def fact(n):
> return reduce(lambda x,y: x*y, range(1,n+1))
>
>
> While Ruby calls it "inject".
>
>
> def fact(n)
> (1..n).inject { |x,y| x*y }
> end
>
>
> Perl 6 has a lot of functional features. IMO the nice thing about its
> version of reduce is the way it's incorporated into the syntax as a
> metaoperator.
Historically, the name reduce was used (first?) in APL, which also
provided it as a meta-operator. op/ would use op to reduce the array
on the right of the meta-operator. (Although, in APL, it could be an
n-dimensional object, not necessarily a 2-dimensional array - the
reduce would compute an (n-1)-dimensional object from it. This could
be used to generate row-sums and column sums. APL was extremely terse,
you could compute almost anything in a single line - Perl golfing
afficionados have never really caught up, although with the addition
of Unicode operators Perl 6 could now go ahead.)
