Composing Procs to explore ideas in Transproc (http://solnic.github.io/transproc/)

proc.rb

class Proc
  def compose(g)
    proc { |*args, &blk| call(g.call(*args, &blk)) }
  end
end

symbolize = ->(x) { x.to_sym }
upcase = ->(x) { x.upcase }
symbolize_and_upcase = symbolize.compose(upcase)

%w(alice bob carol).map(&symbolize_and_upcase)
#=> [:ALICE, :BOB, :CAROL]

# Or, without monkey-patching:

require 'delegate'

class Superproc < SimpleDelegator
  def compose(g)
    proc { |*args, &blk| call(g.call(*args, &blk)) }
  end
end

symbolize = Superproc.new(proc { |x| x.to_sym })
upcase = Superproc.new(proc { |x| x.upcase })
symbolize_and_upcase = symbolize.compose(upcase)

%w(alice bob carol).map(&symbolize_and_upcase)
#=> [:ALICE, :BOB, :CAROL]

# We could also steal `complement` from Clojure...

class Proc
  def !
    proc { |*args, &blk| !call(*args, &blk) }
  end
end

even = ->(x) { x.even? }
odd = !even

(1..10).select(&odd)
#=> [1, 3, 5, 7, 9]