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(.module:
[lux #*
[abstract
[equivalence (#+ Equivalence)]
[functor (#+ Functor)]]
[data
[collection
["." list ("#;." monoid functor)]]]])
(type: #export (Queue a)
{#front (List a)
#rear (List a)})
(def: #export empty
Queue
{#front (list)
#rear (list)})
(def: #export (from-list entries)
(All [a] (-> (List a) (Queue a)))
{#front entries
#rear (list)})
(def: #export (to-list queue)
(All [a] (-> (Queue a) (List a)))
(let [(^slots [#front #rear]) queue]
(list;compose front (list.reverse rear))))
(def: #export peek
(All [a] (-> (Queue a) (Maybe a)))
(|>> (get@ #front) list.head))
(def: #export (size queue)
(All [a] (-> (Queue a) Nat))
(let [(^slots [#front #rear]) queue]
(n/+ (list.size front)
(list.size rear))))
(def: #export empty?
(All [a] (-> (Queue a) Bit))
(|>> (get@ #front) list.empty?))
(def: #export (member? Equivalence<a> queue member)
(All [a] (-> (Equivalence a) (Queue a) a Bit))
(let [(^slots [#front #rear]) queue]
(or (list.member? Equivalence<a> front member)
(list.member? Equivalence<a> rear member))))
(def: #export (pop queue)
(All [a] (-> (Queue a) (Queue a)))
(case (get@ #front queue)
(^ (list)) ## Empty...
queue
(^ (list _)) ## Front has dried up...
(|> queue
(set@ #front (list.reverse (get@ #rear queue)))
(set@ #rear (list)))
(^ (list& _ front')) ## Consume front!
(|> queue
(set@ #front front'))))
(def: #export (push val queue)
(All [a] (-> a (Queue a) (Queue a)))
(case (get@ #front queue)
#.Nil
(set@ #front (list val) queue)
_
(update@ #rear (|>> (#.Cons val)) queue)))
(structure: #export (equivalence Equivalence<a>)
(All [a] (-> (Equivalence a) (Equivalence (Queue a))))
(def: (= qx qy)
(:: (list.equivalence Equivalence<a>) = (to-list qx) (to-list qy))))
(structure: #export functor (Functor Queue)
(def: (map f fa)
{#front (|> fa (get@ #front) (list;map f))
#rear (|> fa (get@ #rear) (list;map f))}))
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