Comments

diff --git a/compiler/typecheck/TcDeriv.lhs b/compiler/typecheck/TcDeriv.lhs
index af53740..4bad739 100644 (file)
--- a/compiler/typecheck/TcDeriv.lhs
+++ b/compiler/typecheck/TcDeriv.lhs
@@ -420,6 +420,7 @@ baleOut err = addErrTc err >> returnM (Nothing, Nothing)
 \begin{code}
 mkDataTypeEqn orig gla_exts tvs cls cls_tys tycon tc_args rep_tc rep_tc_args
   | Just err <- checkSideConditions gla_exts cls cls_tys rep_tc
+       -- NB: pass the *representation* tycon to checkSideConditions
   = baleOut (derivingThingErr cls cls_tys (mkTyConApp tycon tc_args) err)
 
   | otherwise 
@@ -496,7 +497,11 @@ sideConditions
        (dataClassKey,     cond_glaExts `andCond` cond_std)
     ]
 
-type Condition = (Bool, TyCon) -> Maybe SDoc   -- Nothing => OK
+type Condition = (Bool, TyCon) -> Maybe SDoc
+       -- Bool is gla-exts flag
+       -- TyCon is the *representation* tycon if the 
+       --      data type is an indexed one
+       -- Nothing => OK
 
 orCond :: Condition -> Condition -> Condition
 orCond c1 c2 tc