import Maybes
import Util
import FastString
-
-import Maybe
\end{code}
-> [FamInstMatch] -- Successful matches
lookupFamInstEnv
- = lookup_fam_inst_env match
+ = lookup_fam_inst_env match True
where
match _ tpl_tvs tpl_tys tys = tcMatchTys tpl_tvs tpl_tys tys
-- unique supply to hand
lookupFamInstEnvConflicts envs fam_inst skol_tvs
- = lookup_fam_inst_env my_unify envs fam tys'
+ = lookup_fam_inst_env my_unify False envs fam tys'
where
inst_tycon = famInstTyCon fam_inst
(fam, tys) = expectJust "FamInstEnv.lookuFamInstEnvConflicts"
| otherwise = not (old_rhs `tcEqType` new_rhs)
where
old_tycon = famInstTyCon old_fam_inst
- old_rhs = mkTyConApp old_tycon (substTyVars subst (tyConTyVars old_tycon))
+ old_tvs = tyConTyVars old_tycon
+ old_rhs = mkTyConApp old_tycon (substTyVars subst old_tvs)
new_rhs = mkTyConApp inst_tycon (substTyVars subst skol_tvs)
\end{code}
While @lookupFamInstEnv@ uses a one-way match, the next function
-@lookupFamInstEnvUnify@ uses two-way matching (ie, unification). This is
+@lookupFamInstEnvConflicts@ uses two-way matching (ie, unification). This is
needed to check for overlapping instances.
For class instances, these two variants of lookup are combined into one
-> [Type] -- Target to match against
-> Maybe TvSubst
+type OneSidedMatch = Bool -- Are optimisations that are only valid for
+ -- one sided matches allowed?
+
lookup_fam_inst_env -- The worker, local to this module
:: MatchFun
+ -> OneSidedMatch
-> FamInstEnvs
-> TyCon -> [Type] -- What we are looking for
-> [FamInstMatch] -- Successful matches
-lookup_fam_inst_env match_fun (pkg_ie, home_ie) fam tys
+lookup_fam_inst_env match_fun one_sided (pkg_ie, home_ie) fam tys
| not (isOpenTyCon fam)
= []
| otherwise
--------------
rough_tcs = roughMatchTcs match_tys
- all_tvs = all isNothing rough_tcs
+ all_tvs = all isNothing rough_tcs && one_sided
--------------
lookup env = case lookupUFM env fam of