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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/.
(;module:
lux
(lux (control functor
monad
comonad)
[compiler #+ with-gensyms]
(macro ["s" syntax #+ syntax: Syntax])
(data (struct [list "List/" Monad<List>])
bool)
(codata [cont #+ @lazy Cont])))
## [Types]
(type: #export (Stream a)
(Cont [a (Stream a)]))
## [Utils]
(def: (cycle' x xs init full)
(All [a]
(-> a (List a) a (List a) (Stream a)))
(case xs
#;Nil (@lazy [x (cycle' init full init full)])
(#;Cons x' xs') (@lazy [x (cycle' x' xs' init full)])))
## [Functions]
(def: #export (iterate f x)
(All [a]
(-> (-> a a) a (Stream a)))
(@lazy [x (iterate f (f x))]))
(def: #export (repeat x)
(All [a]
(-> a (Stream a)))
(@lazy [x (repeat x)]))
(def: #export (cycle xs)
(All [a]
(-> (List a) (Maybe (Stream a))))
(case xs
#;Nil #;None
(#;Cons x xs') (#;Some (cycle' x xs' x xs'))))
(do-template [<name> <return> <part>]
[(def: #export (<name> s)
(All [a] (-> (Stream a) <return>))
(let [[h t] (cont;run s)]
<part>))]
[head a h]
[tail (Stream a) t])
(def: #export (at idx s)
(All [a] (-> Nat (Stream a) a))
(let [[h t] (cont;run s)]
(if (n.> +0 idx)
(at (n.dec idx) t)
h)))
(do-template [<taker> <dropper> <splitter> <pred-type> <pred-test> <pred-step>]
[(def: #export (<taker> pred xs)
(All [a]
(-> <pred-type> (Stream a) (List a)))
(let [[x xs'] (cont;run xs)]
(if <pred-test>
(list& x (<taker> <pred-step> xs'))
(list))))
(def: #export (<dropper> pred xs)
(All [a]
(-> <pred-type> (Stream a) (Stream a)))
(let [[x xs'] (cont;run xs)]
(if <pred-test>
(<dropper> <pred-step> xs')
xs)))
(def: #export (<splitter> pred xs)
(All [a]
(-> <pred-type> (Stream a) [(List a) (Stream a)]))
(let [[x xs'] (cont;run xs)]
(if <pred-test>
(let [[tail next] (<splitter> <pred-step> xs')]
[(#;Cons [x tail]) next])
[(list) xs])))]
[take-while drop-while split-while (-> a Bool) (pred x) pred]
[take drop split Nat (n.> +0 pred) (n.dec pred)]
)
(def: #export (unfold step init)
(All [a b]
(-> (-> a [a b]) a (Stream b)))
(let [[next x] (step init)]
(@lazy [x (unfold step next)])))
(def: #export (filter p xs)
(All [a] (-> (-> a Bool) (Stream a) (Stream a)))
(let [[x xs'] (cont;run xs)]
(if (p x)
(@lazy [x (filter p xs')])
(filter p xs'))))
(def: #export (partition p xs)
(All [a] (-> (-> a Bool) (Stream a) [(Stream a) (Stream a)]))
[(filter p xs) (filter (complement p) xs)])
## [Structures]
(struct: #export _ (Functor Stream)
(def: (map f fa)
(let [[h t] (cont;run fa)]
(@lazy [(f h) (map f t)]))))
(struct: #export _ (CoMonad Stream)
(def: functor Functor<Stream>)
(def: unwrap head)
(def: (split wa)
(let [[head tail] (cont;run wa)]
(@lazy [wa (split tail)]))))
## [Pattern-matching]
(syntax: #export (^stream& {patterns (s;form (s;many s;any))} body {branches (s;some s;any)})
{#;doc (doc "Allows destructuring of streams in pattern-matching expressions."
"Caveat emptor: Only use it for destructuring, and not for testing values within the streams."
(let [(^stream& x y z _tail) (some-stream-func 1 2 3)]
(func x y z)))}
(with-gensyms [g!s]
(let [body+ (` (let [(~@ (List/join (List/map (lambda [pattern]
(list (` [(~ pattern) (~ g!s)])
(` (cont;run (~ g!s)))))
patterns)))]
(~ body)))]
(wrap (list& g!s body+ branches)))))
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