From: "pabloh (Pablo Herrero)" <pablodherrero@...>
Date: 2012-04-13T08:59:12+09:00
Subject: [ruby-core:44323] [ruby-trunk - Feature #6284] Add composition for procs


Issue #6284 has been updated by pabloh (Pablo Herrero).


=begin

aprescott (Adam Prescott) wrote:
> See also: http://web.archive.org/web/20101228224741/http://drmcawesome.com/FunctionCompositionInRuby


Maybe #| could be a possibility. (Without implementing #> or #<).

But I find the article's proposition about the chaining order a bit missleading:

    transform = add1 | sub3 | negate

For me that feels more like "piping"  ((|add1|)) to ((|sub3|)) to ((|negate|)), from left to right, not the other way around.


If we choose to take that path I think the following code would be a plausible implementation:

    class Proc
      def | block
        proc { |*args| block.to_proc.call( self.call(*args) ) }
      end
    end
    
    class Symbol
      def | block
        self.to_proc | block
      end
    end
=end
----------------------------------------
Feature #6284: Add composition for procs
https://bugs.ruby-lang.org/issues/6284#change-25869

Author: pabloh (Pablo Herrero)
Status: Assigned
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: 2.0.0


=begin
It would be nice to be able to compose procs like functions in functional programming languages:

    to_camel = :capitalize.to_proc
    add_header = ->val {"Title: " + val}

    format_as_title = add_header << to_camel << :strip

instead of:

    format_as_title = lambda {|val| "Title: " + val.strip.capitalize }


It's pretty easy to implement in pure ruby:

  class Proc
    def << block
      proc { |*args| self.call( block.to_proc.call(*args) ) }
    end
  end
=end


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