Issue #6284 has been updated by rits (First Last).


proc composition is not commutative, so the operator should:

1. not imply commutativity
2. not conceal the order of application

i.e. the operator should be visually asymmetrical with clear directionality

e.g. <<, <<<, <-

a << b << c = a(b(c(x))) right associative

perhaps it also makes sense to have an opposite direction, left associative version: c >> b >> a = a(b(c(x)))


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Feature #6284: Add composition for procs
https://bugs.ruby-lang.org/issues/6284#change-34294

Author: pabloh (Pablo Herrero)
Status: Feedback
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: 
Target version: next minor


=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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