p8

class Lisp
  Fs = {
    :label => lambda {|name,value|  Fs[name] = lambda { value } },
    :car =>   lambda {|sexp|        sexp.first },
    :cdr =>   lambda {|sexp|        sexp.slice(1, sexp.size) },
    :cons =>  lambda {|head,tail|   [head] + tail },
    :atom =>  lambda {|sexp|        !sexp.is_a?(Array)  },
    :eq =>    lambda {|a,b|         a == b },
    :if =>    lambda {|cnd,thn,els| cnd ? thn : els }
  }