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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/.
(;import lux
(lux (control (functor #as F #refer #all)
(monad #as M #refer #all)
(comonad #as CM #refer #all))
(meta lux
macro
syntax)
(data (list #as l #refer (#only list list& List/Monad))
(number (int #open ("i" Int/Number Int/Ord)))
bool)
(codata (lazy #as L #refer #all))))
## [Types]
(deftype #export (Stream a)
(Lazy (, a (Stream a))))
## [Utils]
(def (cycle' x xs init full)
(All [a]
(-> a (List a) a (List a) (Stream a)))
(case xs
#;Nil (cycle' init full init full)
(#;Cons [y xs']) (... [x (cycle' y xs' init full)])))
## [Functions]
(def #export (iterate f x)
(All [a]
(-> (-> a a) a (Stream a)))
(... [x (iterate f (f x))]))
(def #export (repeat x)
(All [a]
(-> a (Stream a)))
(... [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] (! s)]
<part>))]
[head a h]
[tail (Stream a) t])
(def #export (@ idx s)
(All [a] (-> Int (Stream a) a))
(let [[h t] (! s)]
(if (i> idx 0)
(@ (i+ -1 idx) t)
h)))
(do-template [<taker> <dropper> <splitter> <det-type> <det-test> <det-step>]
[(def #export (<taker> det xs)
(All [a]
(-> <det-type> (Stream a) (List a)))
(let [[x xs'] (! xs)]
(if <det-test>
(list& x (<taker> <det-step> xs'))
(list))))
(def #export (<dropper> det xs)
(All [a]
(-> <det-type> (Stream a) (Stream a)))
(let [[x xs'] (! xs)]
(if <det-test>
(<dropper> <det-step> xs')
xs)))
(def #export (<splitter> det xs)
(All [a]
(-> <det-type> (Stream a) (, (List a) (Stream a))))
(let [[x xs'] (! xs)]
(if <det-test>
(let [[tail next] (<splitter> <det-step> xs')]
[(#;Cons [x tail]) next])
[(list) xs])))]
[take-while drop-while split-with (-> a Bool) (det x) det]
[take drop split Int (i> det 0) (i+ -1 det)]
)
(def #export (unfold step init)
(All [a b]
(-> (-> a (, a b)) a (Stream b)))
(let [[next x] (step init)]
(... [x (unfold step next)])))
(def #export (filter p xs)
(All [a] (-> (-> a Bool) (Stream a) (Stream a)))
(let [[x xs'] (! xs)]
(if (p x)
(... [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]
(defstruct #export Stream/Functor (Functor Stream)
(def (F;map f fa)
(let [[h t] (! fa)]
(... [(f h) (map f t)]))))
(defstruct #export Stream/CoMonad (CoMonad Stream)
(def CM;_functor Stream/Functor)
(def CM;unwrap head)
(def (CM;split wa)
(:: Stream/Functor (F;map repeat wa))))
## [Pattern-matching]
(defsyntax #export (\stream body [patterns' (+^ id^)])
(do Lux/Monad
[patterns (map% Lux/Monad macro-expand-1 patterns')
g!s (gensym "s")
#let [patterns+ (: (List AST)
(do List/Monad
[pattern (l;reverse patterns)]
(list (` [(~ pattern) (~ g!s)]) (` (L;! (~ g!s))))))]]
(wrap (list g!s (` (;let [(~@ patterns+)] (~ body)))))))
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