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continuation.cljc
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continuation.cljc
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;; Copyright (c) 2014-2015 Andrey Antukh <niwi@niwi.nz>
;; Copyright (c) 2014-2015 Alejandro Gómez <alejandro@dialelo.com>
;; All rights reserved.
;;
;; Redistribution and use in source and binary forms, with or without
;; modification, are permitted provided that the following conditions
;; are met:
;;
;; 1. Redistributions of source code must retain the above copyright
;; notice, this list of conditions and the following disclaimer.
;; 2. Redistributions in binary form must reproduce the above copyright
;; notice, this list of conditions and the following disclaimer in the
;; documentation and/or other materials provided with the distribution.
;;
;; THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
;; IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
;; OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
;; IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
;; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
;; NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
;; DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
;; THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
;; (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
;; THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
(ns cats.monad.continuation
"The Continuation Monad."
(:require [cats.protocols :as proto])
#?(:clj
(:require [cats.core :refer [with-monad]])
:cljs
(:require-macros [cats.core :refer (with-monad)])))
(declare continuation-monad)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Type constructors and functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(deftype Continuation [mfn]
proto/Context
(get-context [_] continuation-monad)
#?(:clj clojure.lang.IFn
:cljs cljs.core/IFn)
(#?(:clj invoke :cljs -invoke) [self seed]
(mfn seed)))
(alter-meta! #'->Continuation assoc :private true)
(defn continuation
"Default constructor for continuation."
[mfn]
(Continuation. mfn))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Monad definition
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(def continuation-monad
(reify
proto/Monad
(mreturn [_ v]
(Continuation. (fn [c] (c v))))
(mbind [_ self mf]
(Continuation. (fn [c]
(self (fn [v]
((mf v) c))))))))
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Continuation monad functions
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
(defn run-cont
"Given a Continuation instance, execute the
wrapped computation and return its value."
[cont]
(with-monad continuation-monad
(cont identity)))
(defn call-cc
[f]
(continuation
(fn [cc]
(let [k (fn [a]
(continuation (fn [_] (cc a))))]
((f k) cc)))))