From: Tanaka Akira <akr@...17n.org>
Date: 2003-01-22T16:01:05+09:00
Subject: Re: Lisp in Ruby?

In article <1c5d01c2c1e2$d76279c0$6401a8c0@MELONBALLER>,
  "Chris Pine" <nemo@hellotree.com> writes:

> Has anyone written a Lisp interpreter in Ruby?  Or even better, a Joy
> interpreter?

10 minutes Lisp (or lambda calculus) interpreter in Ruby:

def eval(exp, env)
  case exp 
  when Array 
    case exp.first
    when :lambda
      lambda {|x|
        env2 = env.dup 
        env2[exp[1]] = x
        eval(exp[2], env2)
      }
    else
      eval(exp[0], env).call(eval(exp[1], env))
    end
  when Symbol
    env[exp]
  else 
    exp # constant
  end
end

p eval([:succ, 1], {:succ => lambda {|x| x + 1}})
-- 
Tanaka Akira