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(.module:
[lux #*
[abstract
[functor (#+ Functor)]
[apply (#+ Apply)]
[monad (#+ Monad do)]]
[control
["." function]
[parser
["s" code]]]
[macro (#+ with-gensyms)
["." code]
[syntax (#+ syntax:)]]])
(type: #export (Cont i o)
{#.doc "Continuations."}
(-> (-> i o) o))
(def: #export (continue next cont)
{#.doc "Continues a continuation thunk."}
(All [i o] (-> (-> i o) (Cont i o) o))
(cont next))
(def: #export (run cont)
{#.doc "Forces a continuation thunk to be evaluated."}
(All [a] (-> (Cont a a) a))
(cont function.identity))
(def: #export (call/cc f)
{#.doc "Call with current continuation."}
(All [a b z]
(-> (-> (-> a (Cont b z))
(Cont a z))
(Cont a z)))
(function (_ k)
(f (function (_ a) (function (_ _) (k a)))
k)))
(syntax: #export (pending expr)
{#.doc (doc "Turns any expression into a function that is pending a continuation."
(pending (some-function some-input)))}
(with-gensyms [g!_ g!k]
(wrap (list (` (.function ((~ g!_) (~ g!k)) ((~ g!k) (~ expr))))))))
(def: #export (reset scope)
(All [i o] (-> (Cont i i) (Cont i o)))
(function (_ k)
(k (run scope))))
(def: #export (shift f)
(All [a]
(-> (-> (-> a (Cont a a))
(Cont a a))
(Cont a a)))
(function (_ oc)
(f (function (_ a) (function (_ ic) (ic (oc a))))
function.identity)))
(structure: #export functor (All [o] (Functor (All [i] (Cont i o))))
(def: (map f fv)
(function (_ k) (fv (function.compose k f)))))
(structure: #export apply (All [o] (Apply (All [i] (Cont i o))))
(def: &functor ..functor)
(def: (apply ff fv)
(function (_ k)
(|> (k (f v))
(function (_ v)) fv
(function (_ f)) ff))))
(structure: #export monad (All [o] (Monad (All [i] (Cont i o))))
(def: &functor ..functor)
(def: (wrap value)
(function (_ k) (k value)))
(def: (join ffa)
(function (_ k)
(ffa (continue k)))))
(def: #export (portal init)
(All [i o z]
(-> i
(Cont [(-> i (Cont o z))
i]
z)))
(call/cc (function (_ k)
(do ..monad
[#let [nexus (function (nexus val)
(k [nexus val]))]
_ (k [nexus init])]
(wrap (undefined))))))
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