[Practical] Partial Application in Ruby

curry.rb

require 'deterministic'

class X
  include Deterministic

  def go
    # The `>>` is from Deterministic. It feeds the result
    # of the left side into the right side.

    # get_num >> mcurry(:add, 1) >> mcurry(:double)
    get_num >> _add(1) >> _double
  end

  def get_num
    Success(11)
  end

  def add(x,y)
    Success(x + y)
  end

  def double(x)
    Success(x * 2)
  end

  # A helper to curry an existing instance method
  def mcurry(method_name, *args)
    m = method(method_name).to_proc

    if args.length - m.arity > 1
      raise ArgumentError.new("too many curried arguments for #{method_name} (#{args.length} for #{m.arity}; you need to leave exactly one open)")
    elsif args.length - m.arity == 0
      lambda { m[*args] }
    else
      m.curry[*args]
    end
  end

  # By prepending a method call with _, we can automatically generate
  # a curried lamda version of that intsance method!
  def method_missing(meth, *args, &block)
    name = meth.to_s
    real_method = name[1..-1]
    if name[0] == '_' && self.respond_to?(real_method)
      mcurry(real_method, *args, &block)
    else
      super
    end
  end
end

x = X.new
puts "RESULT: #{x.go.inspect}"