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(;module:
lux
(lux (control eq)
(data (coll [list "List/" Monoid<List>]))))
## [Types]
(type: #export (Queue a)
{#front (List a)
#rear (List a)})
## [Values]
(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/append 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) Bool))
(|>. (get@ [#front]) list;empty?))
(def: #export (member? a/Eq queue member)
(All [a] (-> (Eq a) (Queue a) a Bool))
(let [(^slots [#front #rear]) queue]
(or (list;member? a/Eq front member)
(list;member? a/Eq 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)))
## [Structures]
(struct: #export (Eq<Queue> Eq<a>)
(All [a] (-> (Eq a) (Eq (Queue a))))
(def: (= qx qy)
(:: (list;Eq<List> Eq<a>) = (to-list qx) (to-list qy))))
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