README.md

An alternative to representable functors

The library provides a Memoizer type class similar to Representable (from adjunctions) that is suitable for containers with size known only at runtime. The only difference between those type classes is that Memoizer passes helper information to the tabulate function.

{-# LANGUAGE TypeFamilies #-}

class Memoizer t where
    -- Rep t
    type Arg t

    -- Helps memoizer to know all possible function inputs.
    type DomainHint t

    -- tabulate
    remember :: (Arg t -> a) -> DomainHint t -> t a

    -- index
    recall      :: t a -> Arg t ->       a
    recallMaybe :: t a -> Arg t -> Maybe a

    {-# MINIMAL remember, (recall | recallMaybe) #-}

Instances

Data type	Arg	DomainHint	Does support unsafe indexing?
any Representable Functor	Representable f => Rep f	() (none)
Array, UArray	Ix i => i	Ix i => (i, i) (range of the array)	Yes
boxed/unboxed/storable Vector	Int	Int (length of the array)	Yes
HashMap	(Hashable k, Eq k) => k	(Hashable k, Eq k) => [k] (all the function inputs)
Map	Ord k => k	Ord k => [k] (all the function inputs)
IntMap	Int	[Int] (all the function inputs)

Store comonad

The library also provides StoreT comonad transformer that uses Memoizer under the hood.

data StoreT memoizer w a
    = StoreT (w (memoizer a)) (DomainHint memoizer) (Arg memoizer)

Is there a documentation?

The source code has a few Haddock documentation, so you can run stack haddock to render it.