Fix instance rules for functional dependencies

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

diff --git a/ghc/compiler/typecheck/TcMType.lhs b/ghc/compiler/typecheck/TcMType.lhs
index 3a232b7..6345efb 100644 (file)
--- a/ghc/compiler/typecheck/TcMType.lhs
+++ b/ghc/compiler/typecheck/TcMType.lhs
@@ -89,7 +89,7 @@ import Kind           ( isSubKind )
 
 -- others:
 import TcRnMonad          -- TcType, amongst others
-import FunDeps         ( grow, checkInstFDs )
+import FunDeps         ( grow, checkInstCoverage )
 import Name            ( Name, setNameUnique, mkSysTvName )
 import VarSet
 import DynFlags                ( dopt, DynFlag(..), DynFlags )
@@ -1117,7 +1117,8 @@ checkValidInstance tyvars theta clas inst_tys
        ; checkInstTermination dflags theta inst_tys
        
        -- The Coverage Condition
-       ; checkTc (checkInstFDs theta clas inst_tys)
+       ; checkTc (dopt Opt_AllowUndecideableInstances dflags ||
+                  checkInstCoverage clas inst_tys)
                  (instTypeErr (pprClassPred clas inst_tys) msg)
        }
   where