Re: currying in Ruby

From: David Flanagan [mailto:[e-mail]]
Sent: Wednesday, June 06, 2007 3:35 AM
>I've written a little argument currying module for Procs and Methods.  I
>think my only real contribution here is the use of << and >> operators
>as a shorthand, which I haven't seen done elsewhere.
>
>Anyone care to review the code and comment?
>
>#
># This module defines currying methods and operators for classes which
># have a call method.
>#
># This module automatically includes itself into Proc and Method.
>#
>module Curry
>   # Return a lambda which is equivalent to an invociation of self
>   # with the specified initial arguments.  When only a single argument
>   # is being specified, the >> alias may be simpler to use.
>
>   def set_initial_args(*initial)
>     lambda {|*rest| self.call(*initial.concat(rest))}
>   end
>
>   # Return a lambda which is equivalent to an invociation of self
>   # with the specified final arguments.  When only a single argument
>   # is being specified, the << alias may be simpler
>
>   def set_final_args(*final)
>     lambda {|*rest| self.call(*rest.concat(final))}
>   end
>
>   alias >> set_initial_args
>   alias << set_final_args
>end
>
>class Proc; include Curry; end
>class Method; include Curry; end
>
># Here is some example code.  First with Procs
>
>difference = lambda { |x,y| x-y }
>minus2 = difference << 2                   # Bind y to 2
>tenminus = difference >> 10                # Bind x to 10
>puts minus2[10]       # Prints 8
>puts tenminus[2]      # Prints 8
>

* The usual problem with proc currying: instance_eval (and instance_exec in
Ruby 1.9 and Facets imitation).

* Personally I dislike >> and << syntax. What this should read like? "shift
difference to 10"? And what about currying of "middle" parameters?

* What's wrong with existing currying module[1]? It's syntax is a bit more
verbose, but reads more natural, I think (especially if alias HOLE and
BLACKHOLE with shorter constants).

V.

1. http://rubymurray.rubyforge.org/