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|
(.module:
[library
[lux #*
["@" target]
[abstract
monoid
[apply (#+ Apply)]
["." functor (#+ Functor)]
["." monad (#+ Monad do)]]]])
(type: #export (Writer l a)
{#.doc "Represents a value with an associated 'log' value to record arbitrary information."}
{#log l
#value a})
(def: #export (write l)
{#.doc "Set the log to a particular value."}
(All [l] (-> l (Writer l Any)))
[l []])
(implementation: #export functor
(All [l]
(Functor (Writer l)))
(def: (map f fa)
(let [[log datum] fa]
[log (f datum)])))
(implementation: #export (apply monoid)
(All [l]
(-> (Monoid l) (Apply (Writer l))))
(def: &functor ..functor)
(def: (apply ff fa)
(let [[log1 f] ff
[log2 a] fa]
[(\ monoid compose log1 log2) (f a)])))
(implementation: #export (monad monoid)
(All [l]
(-> (Monoid l) (Monad (Writer l))))
(def: &functor ..functor)
(def: in
(|>> [(\ monoid identity)]))
(def: (join mma)
(let [[log1 [log2 a]] mma]
[(\ monoid compose log1 log2) a])))
(implementation: #export (with monoid monad)
{#.doc (doc "Enhances a monad with Writer functionality.")}
(All [l M] (-> (Monoid l) (Monad M) (Monad (All [a] (M (Writer l a))))))
(def: &functor
(functor.compose (get@ #monad.&functor monad)
..functor))
(def: in
(let [writer (..monad monoid)]
(|>> (\ writer in) (\ monad in))))
(def: (join MlMla)
(do monad
[[l1 Mla] (for {@.old
(: ((:parameter 1) (Writer (:parameter 0) ((:parameter 1) (Writer (:parameter 0) (:parameter 2)))))
MlMla)}
## On new compiler
MlMla)
[l2 a] Mla]
(in [(\ monoid compose l1 l2) a]))))
(def: #export (lift monoid monad)
{#.doc (doc "Wraps a monadic value with Writer machinery.")}
(All [l M a]
(-> (Monoid l) (Monad M)
(-> (M a) (M (Writer l a)))))
(\ monad map (|>> [(\ monoid identity)])))
|
