ArnisL

class Lisp
  def initialize
    @env = { 
      :label => lambda { |(name,val), _| @env[name] = val },
      :quote => lambda { |sexpr, _| sexpr[0] },
      :car   => lambda { |(list), _| list[0] },
      :cdr   => lambda { |(list), _| list.drop 1 },
      :cons  => lambda { |(e,cell), _| [e] + cell },
      :eq    => lambda { |(l,r), _| l == r },
      :if    => lambda { |(cond, thn, els), ctx| eval(cond, ctx) ? eval(thn, ctx) : eval(els, ctx) },