require 'object'

def for_each(list)
  loop do
    yield(list.car)
    list = list.cdr
    return if list.nil?
  end
end

def map(list)
  [].tap do |r|
    loop do
      r << yield(list.car)
      list = list.cdr
      return r if list.nil?
    end
  end
end


class Evalator
  def initialize env
    @env = env
  end

  def myeval(expr)
    if expr.respond_to?(:car)
      fn = expr.car
      args = map(expr.cdr){|e| myeval(e)}
      find(fn).call(*args)
    else
      expr
    end
  end

  def find(sym)
    return @env[sym]
  end
end

if __FILE__ == $0
  e = Evalator.new({:+ => lambda{|*args| args.inject(0){|s,n| s + n}}})
  Cons::list(:+, 1, 2)
  # for_each(Cons::list(:+, 1, 2)){|e| p e}
  # p map(Cons::list(:+, 1, 2)){|e| e}
  p e.myeval(Cons::list(:+, 1, 2))
end