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## Inspired by;
## "The Different Aspects of Monads and Mixins" by Bruno C. d. S. Oliveira
(.module:
[lux #*
[abstract
[hash (#+ Hash)]
[monad (#+ do)]]
[control
["." state (#+ State)]]
[data
["." product]
[collection
["." dictionary (#+ Dictionary)]]]]
["." // #_
["#" mixin (#+ Mixin Recursive)]])
(def: #export memoization
(All [i o]
(Mixin (-> i (State (Dictionary i o) o))))
(function (_ delegate recur)
(function (_ input)
(do state.monad
[memory state.get]
(case (dictionary.get input memory)
(#.Some output)
(wrap output)
#.None
(do @
[output (delegate input)
_ (state.update (dictionary.put input output))]
(wrap output)))))))
(type: #export (Memo i o)
(Recursive i (State (Dictionary i o) o)))
(def: #export (open memo)
{#.doc (doc "Memoization where the memoized results can be re-used accross invocations.")}
(All [i o]
(:let [Memory (Dictionary i o)]
(-> (Memo i o) (-> [Memory i] [Memory o]))))
(let [memo (//.mixin (//.inherit ..memoization (//.from-recursive memo)))]
(function (_ [memory input])
(|> input memo (state.run memory)))))
(def: #export (closed hash memo)
{#.doc (doc "Memoization confined to a single invocation to the function (not counting any subsequent recursive invocations)."
"Memoized results will be re-used during recursive invocations, but cannot be accessed after the main invocation has ended.")}
(All [i o]
(-> (Hash i) (Memo i o) (-> i o)))
(let [memo (//.mixin (//.inherit ..memoization (//.from-recursive memo)))
empty (dictionary.new hash)]
(|>> memo (state.run empty) product.right)))
(def: #export (none hash memo)
{#.doc (doc "No memoization at all."
"This is useful as a test control when measuring the effect of using memoization.")}
(All [i o]
(-> (Hash i) (Memo i o) (-> i o)))
(let [memo (//.mixin (//.from-recursive memo))
empty (dictionary.new hash)]
(|>> memo (state.run empty) product.right)))
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