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|
(.module:
lux
(lux (control ["m" monoid]
["F" functor]
["A" apply]
[monad #+ do Monad]
[eq #+ Eq])))
## [Types]
## (type: (Maybe a)
## #.None
## (#.Some a))
## [Structures]
(struct: #export Monoid<Maybe> (All [a] (m.Monoid (Maybe a)))
(def: identity #.None)
(def: (compose xs ys)
(case xs
#.None ys
(#.Some x) (#.Some x))))
(struct: #export _ (F.Functor Maybe)
(def: (map f ma)
(case ma
#.None #.None
(#.Some a) (#.Some (f a)))))
(struct: #export _ (A.Apply Maybe)
(def: functor Functor<Maybe>)
(def: (apply ff fa)
(case [ff fa]
[(#.Some f) (#.Some a)]
(#.Some (f a))
_
#.None)))
(struct: #export _ (Monad Maybe)
(def: functor Functor<Maybe>)
(def: (wrap x)
(#.Some x))
(def: (join mma)
(case mma
#.None #.None
(#.Some xs) xs)))
(struct: #export (Eq<Maybe> Eq<a>) (All [a] (-> (Eq a) (Eq (Maybe a))))
(def: (= mx my)
(case [mx my]
[#.None #.None]
true
[(#.Some x) (#.Some y)]
(:: Eq<a> = x y)
_
false)))
(struct: #export (MaybeT Monad<M>)
(All [M] (-> (Monad M) (Monad (All [a] (M (Maybe a))))))
(def: functor (F.compose (get@ #monad.functor Monad<M>) Functor<Maybe>))
(def: wrap (|>> (:: Monad<Maybe> wrap) (:: Monad<M> wrap)))
(def: (join MmMma)
(do Monad<M>
[mMma MmMma]
(case mMma
#.None
(wrap #.None)
(#.Some Mma)
Mma))))
(def: #export (lift Monad<M>)
(All [M a] (-> (Monad M) (-> (M a) (M (Maybe a)))))
(monad.lift Monad<M> (:: Monad<Maybe> wrap)))
(macro: #export (default tokens state)
{#.doc "## Allows you to provide a default value that will be used
## if a (Maybe x) value turns out to be #.None.
(default 20 (#.Some 10)) => 10
(default 20 #.None) => 20"}
(case tokens
(^ (list else maybe))
(let [g!temp (: Code [dummy-cursor (#.Symbol ["" ""])])
code (` (case (~ maybe)
(#.Some (~ g!temp))
(~ g!temp)
#.None
(~ else)))]
(#.Right [state (list code)]))
_
(#.Left "Wrong syntax for default")))
(def: #export assume
(All [a] (-> (Maybe a) a))
(|>> (default (undefined))))
|
