replace several 'fromJust's with 'expectJust's

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

diff --git a/ghc/compiler/typecheck/TcUnify.lhs b/ghc/compiler/typecheck/TcUnify.lhs
index 187f055..23cc9e2 100644 (file)
--- a/ghc/compiler/typecheck/TcUnify.lhs
+++ b/ghc/compiler/typecheck/TcUnify.lhs
@@ -67,7 +67,7 @@ import VarSet         ( emptyVarSet, mkVarSet, unitVarSet, unionVarSet, elemVarSet, var
 import VarEnv
 import Name            ( Name, isSystemName )
 import ErrUtils                ( Message )
-import Maybes          ( fromJust, isNothing )
+import Maybes          ( expectJust, isNothing )
 import BasicTypes      ( Arity )
 import UniqSupply      ( uniqsFromSupply )
 import Util            ( notNull, equalLength )
@@ -1197,7 +1197,8 @@ checkTauTvUpdate orig_tv orig_ty
             ; case mb_tys' of
                Just tys' -> return (TyConApp tc tys')
                                -- Retain the synonym (the common case)
-               Nothing   -> go (fromJust (tcView (TyConApp tc tys)))
+               Nothing   -> go (expectJust "checkTauTvUpdate" 
+                                       (tcView (TyConApp tc tys)))
                                -- Try again, expanding the synonym
             }
 \end{code}