solveInteract :: InertSet -> Bag (CtFlavor,EvVar) -> TcS InertSet
solveInteract inert ws
= do { dyn_flags <- getDynFlags
- ; can_ws <- foldlBagM (tryPreSolveAndCanon inert) emptyCCan ws
+ ; sctx <- getTcSContext
+
+ ; traceTcS "solveInteract, before clever canonicalization:" $
+ ppr (mapBag (\(ct,ev) -> (ct,evVarPred ev)) ws)
+
+ ; can_ws <- foldlBagM (tryPreSolveAndCanon sctx inert) emptyCCan ws
+
+ ; traceTcS "solveInteract, after clever canonicalization:" $
+ ppr can_ws
+
; solveInteractWithDepth (ctxtStkDepth dyn_flags,0,[]) inert can_ws }
-tryPreSolveAndCanon :: InertSet -> CanonicalCts -> (CtFlavor, EvVar) -> TcS CanonicalCts
+tryPreSolveAndCanon :: SimplContext -> InertSet -> CanonicalCts -> (CtFlavor, EvVar) -> TcS CanonicalCts
-- Checks if this constraint can be immediately solved from a constraint in the
-- inert set or in the previously encountered CanonicalCts and only then
-- canonicalise it. See Note [Avoiding the superclass explosion]
-tryPreSolveAndCanon is cts_acc (fl,ev_var)
+tryPreSolveAndCanon sctx is cts_acc (fl,ev_var)
| ClassP clas tys <- evVarPred ev_var
+ , not $ simplEqsOnly sctx -- And we *can* discharge constraints from other constraints
= do { let (relevant_inert_dicts,_) = getRelevantCts clas (inert_dicts is)
; b <- dischargeFromCans (cts_acc `unionBags` relevant_inert_dicts)
(fl,ev_var,clas,tys)