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## Copyright (c) Eduardo Julian. All rights reserved.
## This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
## If a copy of the MPL was not distributed with this file,
## You can obtain one at http://mozilla.org/MPL/2.0/.
(;import lux
(lux/control (monoid #as m #refer #all)
(functor #as F #refer #all)
(monad #as M #refer #all)))
## [Types]
(deftype #export (Writer l a)
(, l a))
## [Structures]
(defstruct #export Writer/Functor (All [l]
(Functor (Writer l)))
(def (map f fa)
(let [[log datum] fa]
[log (f datum)])))
(defstruct #export (Writer/Monad mon) (All [l]
(-> (Monoid l) (Monad (Writer l))))
(def _functor Writer/Functor)
(def (wrap x)
[(:: mon unit) x])
(def (join mma)
(let [[log1 [log2 a]] mma]
[(:: mon (++ log1 log2)) a])))
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