assoc-memoize.coffee

_.mixin assoc: (assoc_list, key, val) -> assoc_list.concat [[key, val]]
_.mixin lookup: (assoc_list, key) -> _.find(assoc_list, ([k, v]) -> k is key)?[1]

# Memoizes a one-arg function using JS value equality to check for argument
# equality. This is useful if you want to memoize a function that takes
# objects. It's slower though, since it has to search for seen args in an array
# (which takes time proportional to the number of previously seen args).
_.mixin memoizeByEquality: (f) ->
  seen = []
  (arg) ->
    if (res = _.lookup seen, arg)?
      res
    else
      new_res = f arg
      seen = _.assoc seen, arg, new_res
      new_res