}
where
substRules eq1 eq2
- = do { -- try the SubstFam rule
- optEqs <- applySubstFam eq1 eq2
+ = do {traceTc $ hang (ptext (sLit "Trying subst rules with"))
+ 4 (ppr eq1 $$ ppr eq2)
+
+ -- try the SubstFam rule
+ ; optEqs <- applySubstFam eq1 eq2
; case optEqs of
Just (eqs, skolems) -> return (eqs, [], skolems)
Nothing -> do
-> TcM (Maybe ([RewriteInst], TyVarSet))
applySubstFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1})
eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
+
+ -- rule matches => rewrite
| fam1 == fam2 && tcEqTypes args1 args2 &&
(isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
-- !!!TODO: tcEqTypes is insufficient as it does not look through type synonyms
; eq2' <- deriveEqInst eq2 lhs rhs co2'
; liftM Just $ normEqInst eq2'
}
+
+ -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
+ | fam1 == fam2 && tcEqTypes args1 args2 &&
+ (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2))
+ = return $ Just ([eq2], emptyVarSet)
+
where
lhs = rwi_right eq1
rhs = rwi_right eq2
co1 = eqInstCoType (rwi_co eq1)
co2 = rwi_co eq2
+
applySubstFam _ _ = return Nothing
\end{code}
-> TcM (Maybe ([RewriteInst], TyVarSet))
applySubstVarVar eq1@(RewriteVar {rwi_var = tv1})
eq2@(RewriteVar {rwi_var = tv2})
+
+ -- rule matches => rewrite
| tv1 == tv2 &&
(isWantedRewriteInst eq2 || not (isWantedRewriteInst eq1))
= do { co2' <- mkRightTransEqInstCo co2 co1 (lhs, rhs)
; eq2' <- deriveEqInst eq2 lhs rhs co2'
; liftM Just $ normEqInst eq2'
}
+
+ -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
+ | tv1 == tv2 &&
+ (isWantedRewriteInst eq1 || not (isWantedRewriteInst eq2))
+ = return $ Just ([eq2], emptyVarSet)
+
where
lhs = rwi_right eq1
rhs = rwi_right eq2
co1 = eqInstCoType (rwi_co eq1)
co2 = rwi_co eq2
+
applySubstVarVar _ _ = return Nothing
\end{code}
\begin{code}
applySubstVarFam :: RewriteInst -> RewriteInst -> TcM (Maybe RewriteInst)
+
+ -- rule matches => rewrite
applySubstVarFam eq1@(RewriteVar {rwi_var = tv1})
eq2@(RewriteFam {rwi_fam = fam2, rwi_args = args2})
| tv1 `elemVarSet` tyVarsOfTypes args2
rhs2 = rwi_right eq2
co1 = eqInstCoType (rwi_co eq1)
co2 = rwi_co eq2
+
+ -- rule would match with eq1 and eq2 swapped => put eq2 into todo list
+applySubstVarFam eq1@(RewriteFam {rwi_fam = fam1, rwi_args = args1})
+ eq2@(RewriteVar {rwi_var = tv2})
+ | tv2 `elemVarSet` tyVarsOfTypes args1
+ = return $ Just eq2
+
applySubstVarFam _ _ = return Nothing
\end{code}