+ ; let givens = red_givens env
+ (given_eqs0, given_dicts0) = partition isEqInst givens
+ (wanted_eqs0, wanted_dicts0) = partition isEqInst wanteds
+
+ -- We want to add as wanted equalities those that (transitively)
+ -- occur in superclass contexts of wanted class constraints.
+ -- See Note [Ancestor Equalities]
+ ; ancestor_eqs <- ancestorEqualities wanted_dicts0
+ ; let wanted_eqs = wanted_eqs0 ++ ancestor_eqs
+ ; traceTc $ text "reduceContext: ancestor eqs" <+> ppr ancestor_eqs
+
+ -- 1. Normalise the *given* *equality* constraints
+ ; (given_eqs, eliminate_skolems) <- normaliseGivenEqs given_eqs0
+
+ -- 2. Normalise the *given* *dictionary* constraints
+ -- wrt. the toplevel and given equations
+ ; (given_dicts, given_binds) <- normaliseGivenDicts given_eqs
+ given_dicts0
+
+ -- 5. Build the Avail mapping from "given_dicts"
+ -- Add dicts refined by the current type refinement
+ ; (init_state, extra_givens) <- getLIE $ do
+ { init_state <- foldlM addGiven emptyAvails given_dicts
+ ; let reft = red_reft env
+ ; if isEmptyRefinement reft then return init_state
+ else foldlM (addRefinedGiven reft)
+ init_state given_dicts }
+
+ -- *** ToDo: what to do with the "extra_givens"? For the
+ -- moment I'm simply discarding them, which is probably wrong
+
+ -- 7. Normalise the *wanted* *dictionary* constraints
+ -- wrt. the toplevel and given equations
+ -- NB: normalisation includes zonking as part of what it does
+ -- so it's important to do it after any unifications
+ -- that happened as a result of the addGivens
+ ; (wanted_dicts,normalise_binds1) <- normaliseWantedDicts given_eqs wanted_dicts0
+
+ -- 6. Solve the *wanted* *dictionary* constraints
+ -- This may expose some further equational constraints...
+ ; (avails, extra_eqs) <- getLIE (reduceList env wanted_dicts init_state)
+ ; let (binds, irreds1, needed_givens) = extractResults avails wanted_dicts
+ ; traceTc $ text "reduceContext extractresults" <+> vcat
+ [ppr avails,ppr wanted_dicts,ppr binds,ppr needed_givens]
+
+ -- *** ToDo: what to do with the "extra_eqs"? For the
+ -- moment I'm simply discarding them, which is probably wrong
+
+ -- 3. Solve the *wanted* *equation* constraints
+ ; eq_irreds0 <- solveWantedEqs given_eqs wanted_eqs
+
+ -- 4. Normalise the *wanted* equality constraints with respect to
+ -- each other
+ ; eq_irreds <- normaliseWantedEqs eq_irreds0
+
+ -- 8. Substitute the wanted *equations* in the wanted *dictionaries*
+ ; (irreds,normalise_binds2) <- substEqInDictInsts eq_irreds irreds1
+
+ -- 9. eliminate the artificial skolem constants introduced in 1.
+ ; eliminate_skolems
+
+ -- Figure out whether we should go round again
+ -- My current plan is to see if any of the mutable tyvars in
+ -- givens or irreds has been filled in by improvement.
+ -- If so, there is merit in going around again, because
+ -- we may make further progress
+ --
+ -- ToDo: is it only mutable stuff? We may have exposed new
+ -- equality constraints and should probably go round again
+ -- then as well. But currently we are dropping them on the
+ -- floor anyway.
+
+ ; let all_irreds = irreds ++ eq_irreds
+ ; improved <- anyM isFilledMetaTyVar $ varSetElems $
+ tyVarsOfInsts (givens ++ all_irreds)
+
+ -- The old plan (fragile)
+ -- improveed = availsImproved avails
+ -- || (not $ isEmptyBag normalise_binds1)
+ -- || (not $ isEmptyBag normalise_binds2)
+ -- || (any isEqInst irreds)
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