Created
September 12, 2017 15:06
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Heterogenous list (product) that applies a type
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{-# LANGUAGE PolyKinds, DataKinds, GADTs, TypeOperators, ConstraintKinds, RankNTypes, MultiParamTypeClasses, FlexibleInstances, FlexibleContexts, UndecidableInstances #-} | |
import Data.Proxy | |
import Data.Functor.Identity | |
import GHC.Exts (Constraint) | |
data HKList :: (k -> *) -> [k] -> * where | |
Nil :: HKList f '[] | |
(:*) :: f x -> HKList f xs -> HKList f (x ': xs) | |
-- From constraints | |
data Dict :: Constraint -> * where | |
Dict :: a => Dict a | |
data Dict1 :: (k -> Constraint) -> k -> * where | |
Dict1 :: c k => Dict1 c k | |
data Has c a where | |
Has :: c a => a -> Has c a | |
type ConstrainedList c = HKList (Has c) | |
-- from constraints | |
newtype a :- b = Sub (a => Dict b) | |
type SList = HKList Proxy | |
class All c xs where | |
dicts :: HKList (Dict1 c) xs | |
instance All c '[] where | |
dicts = Nil | |
instance (All c xs, c x) => All c (x ': xs) where | |
dicts = Dict1 :* dicts | |
zipHKList :: (forall k. f k -> g k -> h k) -> HKList f xs -> HKList g xs -> HKList h xs | |
zipHKList _ Nil Nil = Nil | |
zipHKList f (x :* xs) (y :* ys) = f x y :* zipHKList f xs ys | |
allToHas :: All c xs => HKList Identity xs -> HKList (Has c) xs | |
allToHas xs = zipHKList f dicts xs | |
where | |
f :: Dict1 c k -> Identity k -> Has c k | |
f Dict1 (Identity x) = Has x | |
hasToAll :: HKList (Has c) xs -> Dict (All c xs) | |
hasToAll Nil = Dict | |
hasToAll (Has x :* xs) = | |
case hasToAll xs of | |
Dict -> Dict |
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