Inspired by this moonbase entry…

It would have been nice to just specify bind(f) but that didn’t seem to work as ruby parameters appear to be strictly evaluated.

irb(main):001:0> require 'monad'=> trueirb(main):002:0> def f(x); x + 1; end => nilirb(main):003:0> IdentityMonad.wrap(1).bind(method(:f)).bind{|x| x + 2}.value=> 4irb(main):004:0> 
class IdentityMonad
   attr_reader :value
   def initialize(value)
      @value = value
   end
   def IdentityMonad::wrap(value)
      new(value)
   end
   def pass
      yield @value
   end
   def bind(p=nil,&blk)
      if block_given?
         IdentityMonad::wrap(blk.call(@value))
      else
         IdentityMonad::wrap(p.call(@value))
      end
   end
end