Straightened out implicit coercions for indexed types

[ghc-hetmet.git] / compiler / types / Coercion.lhs

diff --git a/compiler/types/Coercion.lhs b/compiler/types/Coercion.lhs
index 25d04ec..1dbd7f3 100644 (file)
--- a/compiler/types/Coercion.lhs
+++ b/compiler/types/Coercion.lhs
@@ -22,7 +22,7 @@ module Coercion (
         mkSymCoercion, mkTransCoercion,
         mkLeftCoercion, mkRightCoercion, mkInstCoercion, mkAppCoercion,
         mkForAllCoercion, mkFunCoercion, mkInstsCoercion, mkUnsafeCoercion,
-        mkNewTypeCoercion, mkAppsCoercion,
+        mkNewTypeCoercion, mkDataInstCoercion, mkAppsCoercion,
 
         splitNewTypeRepCo_maybe, decomposeCo,
 
@@ -38,10 +38,10 @@ import Type   ( Type, Kind, PredType, substTyWith, mkAppTy, mkForAllTy,
                     mkFunTy, splitAppTy_maybe, splitForAllTy_maybe, coreView,
                     kindView, mkTyConApp, isCoercionKind, isEqPred, mkAppTys,
                     coreEqType, splitAppTys, isTyVarTy, splitTyConApp_maybe,
-                    tyVarsOfType
+                    tyVarsOfType, mkTyVarTys
                   )
-import TyCon      ( TyCon, tyConArity, mkCoercionTyCon, isNewTyCon,
-                    newTyConRhs, newTyConCo, 
+import TyCon      ( TyCon, tyConArity, mkCoercionTyCon, isClosedNewTyCon,
+                    newTyConRhs, newTyConCo_maybe, 
                     isCoercionTyCon, isCoercionTyCon_maybe )
 import Var       ( Var, TyVar, isTyVar, tyVarKind )
 import VarSet     ( elemVarSet )
@@ -323,7 +323,31 @@ mkNewTypeCoercion name tycon tvs rhs_ty
     rhs_eta
       | (ty, ty_args) <- splitAppTys rhs_ty
       = mkAppTys ty (reverse (drop n_eta_tys (reverse ty_args)))
- 
+
+-- Coercion identifying a data/newtype representation type and its family
+-- instance.  It has the form `Co tvs :: F ts :=: R tvs', where `Co' is the
+-- coercion tycon built here, `F' the family tycon and `R' the (derived)
+-- representation tycon.
+--
+mkDataInstCoercion :: Name     -- unique name for the coercion tycon
+                  -> [TyVar]   -- type parameters of the coercion (`tvs')
+                  -> TyCon     -- family tycon (`F')
+                  -> [Type]    -- type instance (`ts')
+                  -> TyCon     -- representation tycon (`R')
+                  -> TyCon     -- => coercion tycon (`Co')
+mkDataInstCoercion name tvs family instTys rep_tycon
+  = mkCoercionTyCon name coArity (mkKindingFun rule)
+  where
+    coArity = length tvs
+
+    rule args = (substTyWith tvs tys $              -- with sigma = [tys/tvs],
+                  TyConApp family instTys,          --       sigma (F ts)
+                TyConApp rep_tycon tys,             --   :=: R tys
+                rest)                               -- surplus arguments
+      where
+        tys  = take coArity args
+        rest = drop coArity args
+
 --------------------------------------
 -- Coercion Type Constructors...
 
@@ -427,7 +451,7 @@ splitNewTypeRepCo_maybe :: Type -> Maybe (Type, Coercion)
 splitNewTypeRepCo_maybe ty 
   | Just ty' <- coreView ty = splitNewTypeRepCo_maybe ty'
 splitNewTypeRepCo_maybe (TyConApp tc tys)
-  | isNewTyCon tc 
+  | isClosedNewTyCon tc 
   = ASSERT( tys `lengthIs` tyConArity tc )     -- splitNewTypeRepCo_maybe only be applied 
                                                 --     to *types* (of kind *)
         case newTyConRhs tc of
@@ -435,6 +459,6 @@ splitNewTypeRepCo_maybe (TyConApp tc tys)
               ASSERT( length tvs == length tys )
              Just (substTyWith tvs tys rep_ty, mkTyConApp co_con tys)
   where
-    co_con = maybe (pprPanic "splitNewTypeRepCo_maybe" (ppr tc)) id (newTyConCo tc)
+    co_con = maybe (pprPanic "splitNewTypeRepCo_maybe" (ppr tc)) id (newTyConCo_maybe tc)
 splitNewTypeRepCo_maybe other = Nothing
 \end{code}