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{-# LANGUAGE DataKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}
module Interpreter.Rep where
import Data.IORef
import GHC.TypeError
import Array
import AST
type family Rep t where
Rep TNil = ()
Rep (TPair a b) = (Rep a, Rep b)
Rep (TEither a b) = Either (Rep a) (Rep b)
Rep (TMaybe t) = Maybe (Rep t)
Rep (TArr n t) = Array n (Rep t)
Rep (TScal sty) = ScalRep sty
Rep (TAccum t) = RepAcSparse t
-- Mutable, and has an O(1) zero.
type family RepAcSparse t where
RepAcSparse TNil = ()
RepAcSparse (TPair a b) = IORef (RepAcDense (TPair a b))
RepAcSparse (TEither a b) = TypeError (Text "Non-sparse coproduct is not a monoid")
RepAcSparse (TMaybe t) = IORef (Maybe (RepAcDense t)) -- allow the value to be dense, because the Maybe's zero can be used for the contents
RepAcSparse (TArr n t) = IORef (RepAcDense (TArr n t)) -- empty array is zero
RepAcSparse (TScal sty) = IORef (ScalRep sty)
RepAcSparse (TAccum t) = TypeError (Text "RepAcSparse: Nested accumulators")
-- Immutable, and does not necessarily have a zero.
type family RepAcDense t where
RepAcDense TNil = ()
RepAcDense (TPair a b) = (RepAcSparse a, RepAcSparse b)
RepAcDense (TEither a b) = Either (RepAcSparse a) (RepAcSparse b)
RepAcDense (TMaybe t) = Maybe (RepAcSparse t)
RepAcDense (TArr n t) = Array n (RepAcSparse t)
RepAcDense (TScal sty) = ScalRep sty
RepAcDense (TAccum t) = TypeError (Text "RepAcDense: Nested accumulators")
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