From: Brian Candler <B.Candler@...>
Date: 2007-03-01T15:35:58+09:00
Subject: Re: Functional programming in Ruby

On Thu, Mar 01, 2007 at 10:35:43AM +0900, James Edward Gray II wrote:
> >proc { |*a|
> >  proc { |iter| iter.call(iter, *a) }.call(
> >    proc { |me, n, f|
> >      if n >= 1
> >        f.call()
> >        me.call(me, n-1, f)
> >      end
> >    }
> >  )
> >}.call(3, proc { puts "hello again" } )
> 
> Wow, those melted my brain.
> 
> I kept thinking I could peel off the outer layer off the factorial  
> one, but I didn't succeed.  Wild stuff.

Here's perhaps a cleaner version:

proc { |n1, f1|
  proc { |func, *args| func.call(func, *args) }.call(
    proc { |me, n, f|
      if n >= 1
        f.call()
        me.call(me, n-1, f)
      end
    }, n1, f1
  )
}.call(3, proc { puts "hello again" } )

Line 2 encapsulates "a function which just calls the function+args you pass
in, except passing the function itself as an extra argument"

Cheers,

Brian.