##   Copyright (c) Eduardo Julian. All rights reserved.
##   The use and distribution terms for this software are covered by the
##   Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
##   which can be found in the file epl-v10.html at the root of this distribution.
##   By using this software in any fashion, you are agreeing to be bound by
##   the terms of this license.
##   You must not remove this notice, or any other, from this software.

(;import lux
         (lux/data state))

## Signatures
(defsig #export (Functor f)
  (: (All [a b]
       (-> (-> a b) (f a) (f b)))
     map))

## Structures
(defstruct #export Maybe:Functor (Functor Maybe)
  (def (map f ma)
    (case ma
      #;None     #;None
      (#;Some a) (#;Some (f a)))))

(defstruct #export List:Functor (Functor List)
  (def (map f ma)
    (case ma
      #;Nil            #;Nil
      (#;Cons [a ma']) (#;Cons [(f a) (map f ma')]))))

(defstruct #export State:Functor (Functor State)
  (def (map f ma)
    (lambda [state]
      (let [[state' a] (ma state)]
        [state' (f a)]))))