math_lisp.coffee

fns =
  '+': (a,b) -> a + b
  '*': (a,b) -> a * b

parse = (input) ->
  JSON.parse(input.replace(/\s/g,",").replace(/\+|\*/g, '"$&"'))

evaluate = (x)->
  if (Array.isArray(x)) # x is an expression
    results = x.map (expression) -> evaluate(expression)
    results[0].apply {}, results[1..-1]
  else if fns[x]
    fns[x]
  else
    x

alert evaluate parse "[* [+ 1 2] 2]"