WIP Accum stuff

1 files changed, 21 insertions, 16 deletions

diff --git a/src/Interpreter/Rep.hs b/src/Interpreter/Rep.hs
index 7add442..680196c 100644
--- a/src/Interpreter/Rep.hs
+++ b/src/Interpreter/Rep.hs
@@ -1,9 +1,9 @@
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UndecidableInstances #-}
 module Interpreter.Rep where
 
 import Data.IORef
-import qualified Data.Vector.Mutable as MV
 import GHC.TypeError
 
 import Array
@@ -17,19 +17,24 @@ type family Rep t where
   Rep (TMaybe t) = Maybe (Rep t)
   Rep (TArr n t) = Array n (Rep t)
   Rep (TScal sty) = ScalRep sty
-  Rep (TAccum t) = IORef (RepAc t)
+  Rep (TAccum t) = RepAcSparse t
 
-type family RepAc t where
-  RepAc TNil = ()
-  RepAc (TPair a b) = (RepAc a, RepAc b)
-  -- This is annoying when working with values of type 'RepAc t', because
-  -- failing a pattern match does not generate negative type information.
-  -- However, it works, saves us from having to defining a LEither type
-  -- first-class in the type system with
-  --   Rep (LEither a b) = Maybe (Either a b)
-  -- and it's not even incorrect, in a way.
-  RepAc (TMaybe (TEither a b)) = IORef (Maybe (Either (RepAc a) (RepAc b)))
-  RepAc (TMaybe t) = IORef (Maybe (RepAc t))
-  RepAc (TArr n t) = (Shape n, MV.IOVector (RepAc t))
-  RepAc (TScal sty) = IORef (ScalRep sty)
-  RepAc (TAccum t) = TypeError (Text "Nested accumulators")
+-- 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")