CoffeeScript deep object intersection

deep_intersection.coffee

intersection = (lst) ->
  types = lst.map((x)-> typeof x)
  if types.some((t) -> t != types[0])
    return null

  switch types[0]
    when "object"
      res = {}
      Object.keys(lst[0]).forEach (k) ->
        if lst.every((o) -> k of o)
          intersect = intersection lst.map((o) -> o[k])
          if intersect != null
            res[k] = intersect
      return res
    when "number", "string", "boolean", "function"
      if lst.some((e) -> e.toString() != lst[0].toString())
        return null
      else
        return lst[0]
    else
      throw new Error("unimplemented #{types[0]}")