X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Ftypecheck%2FTcEnv.lhs;h=0f9bf231c8c66b3c2475e73630a82bb4a5657533;hb=289ee3d0daa95445ead578f2b674987a4187993d;hp=ff49db6af6b04448f5a032cbb551f2d397b58b4a;hpb=cd290fc88d35d5a32c994664baa56a5eae250e9e;p=ghc-hetmet.git

diff --git a/compiler/typecheck/TcEnv.lhs b/compiler/typecheck/TcEnv.lhs
index ff49db6..0f9bf23 100644
--- a/compiler/typecheck/TcEnv.lhs
+++ b/compiler/typecheck/TcEnv.lhs
@@ -42,7 +42,10 @@ module TcEnv(
 	topIdLvl, 
 
 	-- New Ids
-	newLocalName, newDFunName, newFamInstTyConName
+	newLocalName, newDFunName, newFamInstTyConName,
+
+        -- Errors
+        famInstNotFound
   ) where
 
 #include "HsVersions.h"
@@ -55,7 +58,6 @@ import TcMType
 import TcType
 import TcGadt
 import qualified Type
-import Id
 import Var
 import VarSet
 import VarEnv
@@ -160,7 +162,21 @@ tcLookupLocatedTyCon :: Located Name -> TcM TyCon
 tcLookupLocatedTyCon = addLocM tcLookupTyCon
 
 -- Look up the representation tycon of a family instance.
--- Return the rep tycon and the corresponding rep args
+--
+-- The match must be unique - ie, match exactly one instance - but the 
+-- type arguments used for matching may be more specific than those of 
+-- the family instance declaration.
+--
+-- Return the instance tycon and its type instance.  For example, if we have
+--
+--  tcLookupFamInst 'T' '[Int]' yields (':R42T', 'Int')
+--
+-- then we have a coercion (ie, type instance of family instance coercion)
+--
+--  :Co:R42T Int :: T [Int] ~ :R42T Int
+--
+-- which implies that :R42T was declared as 'data instance T [a]'.
+--
 tcLookupFamInst :: TyCon -> [Type] -> TcM (TyCon, [Type])
 tcLookupFamInst tycon tys
   | not (isOpenTyCon tycon)
@@ -170,20 +186,8 @@ tcLookupFamInst tycon tys
        ; eps <- getEps
        ; let instEnv = (eps_fam_inst_env eps, tcg_fam_inst_env env)
        ; case lookupFamInstEnv instEnv tycon tys of
-
-	   [(subst, fam_inst)] | variable_only_subst -> 
-	     return (rep_tc, substTyVars subst (tyConTyVars rep_tc))
-		where	-- NB: assumption is that (tyConTyVars rep_tc) is in 
-			--     the domain of the substitution
-		  rep_tc              = famInstTyCon fam_inst
-		  subst_domain        = varEnvElts . getTvSubstEnv $ subst
-		  tvs		      = map (Type.getTyVar "tcLookupFamInst") 
-					    subst_domain
-		  variable_only_subst = all Type.isTyVarTy subst_domain &&
-					sizeVarSet (mkVarSet tvs) == length tvs
-					-- renaming may have no repetitions
-
-	   other -> famInstNotFound tycon tys other
+	   [(fam_inst, rep_tys)] -> return (famInstTyCon fam_inst, rep_tys)
+	   other                 -> famInstNotFound tycon tys other
        }
 \end{code}
 
@@ -636,7 +640,7 @@ Make a name for the dict fun for an instance decl.  It's an *external*
 name, like otber top-level names, and hence must be made with newGlobalBinder.
 
 \begin{code}
-newDFunName :: Class -> [Type] -> SrcLoc -> TcM Name
+newDFunName :: Class -> [Type] -> SrcSpan -> TcM Name
 newDFunName clas (ty:_) loc
   = do	{ index   <- nextDFunIndex
 	; is_boot <- tcIsHsBoot
@@ -650,12 +654,12 @@ newDFunName clas (ty:_) loc
 newDFunName clas [] loc = pprPanic "newDFunName" (ppr clas <+> ppr loc)
 \end{code}
 
-Make a name for the representation tycon of a data/newtype instance.  It's an
+Make a name for the representation tycon of a family instance.  It's an
 *external* name, like otber top-level names, and hence must be made with
 newGlobalBinder.
 
 \begin{code}
-newFamInstTyConName :: Name -> SrcLoc -> TcM Name
+newFamInstTyConName :: Name -> SrcSpan -> TcM Name
 newFamInstTyConName tc_name loc
   = do	{ index <- nextDFunIndex
 	; mod   <- getModule