ruby-pattern-matching.rb

class CasePattern
  def initialize(arr)
    @arr = arr
  end

  def ===(other_arr)
    @arr.zip(other_arr).all?{ |x1, x2| x1 === x2 }
  end

  module ConstructorContext
    def self.___
      CasePattern::Wildcard
    end
  end

  class Wildcard
    def self.===(x)
      true
    end
  end
end

def Pattern(&block)
  CasePattern.new(CasePattern::ConstructorContext.instance_eval(&block))
end


# Examples:

case [1, 'foobarbaz', 999]
when Pattern{[Integer, /foo/, 111]} then "I don't match"
when Pattern{[Integer, /foo/, ___]} then "I match!"
end