[project @ 2004-04-02 13:16:07 by simonpj]

[ghc-hetmet.git] / ghc / compiler / typecheck / Inst.lhs

diff --git a/ghc/compiler/typecheck/Inst.lhs b/ghc/compiler/typecheck/Inst.lhs
index 5e82933..f296e1b 100644 (file)
--- a/ghc/compiler/typecheck/Inst.lhs
+++ b/ghc/compiler/typecheck/Inst.lhs
@@ -695,28 +695,17 @@ lookupInst inst@(LitInst u (HsFractional f from_rat_name) ty loc)
 
 -- Dictionaries
 lookupInst dict@(Dict _ pred@(ClassP clas tys) loc)
-  = do { dflags  <- getDOpts
-       ; if all tcIsTyVarTy tys && 
-            not (dopt Opt_AllowUndecidableInstances dflags)
-               -- Common special case; no lookup
-               -- NB: tcIsTyVarTy... don't look through newtypes!
-               -- Don't take this short cut if we allow undecidable instances
-               -- because we might have "instance T a where ...".
-               -- [That means we need -fallow-undecidable-instances in the 
-               --  client module, as well as the module with the instance decl.]
-         then return NoInstance
-
-         else do
-       { pkg_ie  <- loadImportedInsts clas tys
+  = do { pkg_ie <- loadImportedInsts clas tys
                -- Suck in any instance decls that may be relevant
        ; tcg_env <- getGblEnv
+       ; dflags  <- getDOpts
        ; case lookupInstEnv dflags (pkg_ie, tcg_inst_env tcg_env) clas tys of {
            ([(tenv, (_,_,dfun_id))], []) -> instantiate_dfun tenv dfun_id pred loc ;
            (matches, unifs)              -> do
        { traceTc (text "lookupInst fail" <+> vcat [text "dict" <+> ppr pred,
                                                    text "matches" <+> ppr matches,
                                                    text "unifs" <+> ppr unifs])
-       ; return NoInstance } } } }
+       ; return NoInstance } } }
                -- In the case of overlap (multiple matches) we report
                -- NoInstance here.  That has the effect of making the 
                -- context-simplifier return the dict as an irreducible one.