diff options
Diffstat (limited to 'compiler/typecheck')
| -rw-r--r-- | compiler/typecheck/TcMType.hs | 6 | ||||
| -rw-r--r-- | compiler/typecheck/TcRnTypes.hs | 30 |
2 files changed, 30 insertions, 6 deletions
diff --git a/compiler/typecheck/TcMType.hs b/compiler/typecheck/TcMType.hs index fdb956aedd..99f4475cb6 100644 --- a/compiler/typecheck/TcMType.hs +++ b/compiler/typecheck/TcMType.hs @@ -1432,9 +1432,9 @@ quantifyTyVars gbl_tvs -- NB: All variables in the kind of a covar must not be -- quantified over, as we don't quantify over the covar. - dep_kvs = dVarSetElemsWellScoped $ + dep_kvs = scopedSort $ dVarSetElems $ dep_tkvs `dVarSetMinusVarSet` mono_tvs - -- dVarSetElemsWellScoped: put the kind variables into + -- scopedSort: put the kind variables into -- well-scoped order. -- E.g. [k, (a::k)] not the other way roud @@ -1452,7 +1452,7 @@ quantifyTyVars gbl_tvs -- This block uses level numbers to decide what to quantify -- and emits a warning if the two methods do not give the same answer - ; let dep_kvs2 = dVarSetElemsWellScoped $ + ; let dep_kvs2 = scopedSort $ dVarSetElems $ filterDVarSet (quantifiableTv outer_tclvl) dep_tkvs nondep_tvs2 = filter (quantifiableTv outer_tclvl) $ dVarSetElems (nondep_tkvs `minusDVarSet` dep_tkvs) diff --git a/compiler/typecheck/TcRnTypes.hs b/compiler/typecheck/TcRnTypes.hs index 3c6b8ca685..3bd26e9f76 100644 --- a/compiler/typecheck/TcRnTypes.hs +++ b/compiler/typecheck/TcRnTypes.hs @@ -1542,6 +1542,10 @@ data TcIdSigInst -- No need to keep track of whether they are truly lexically -- scoped because the renamer has named them uniquely -- See Note [Binding scoped type variables] in TcSigs + -- + -- NB: The order of sig_inst_skols is irrelevant + -- for a CompleteSig, but for a PartialSig see + -- Note [Quantified varaibles in partial type signatures] , sig_inst_theta :: TcThetaType -- Instantiated theta. In the case of a @@ -1553,9 +1557,9 @@ data TcIdSigInst -- Relevant for partial signature only , sig_inst_wcs :: [(Name, TcTyVar)] - -- Like sig_inst_skols, but for wildcards. The named - -- wildcards scope over the binding, and hence their - -- Names may appear in type signatures in the binding + -- Like sig_inst_skols, but for /named/ wildcards (_a etc). + -- The named wildcards scope over the binding, and hence + -- their Names may appear in type signatures in the binding , sig_inst_wcx :: Maybe TcType -- Extra-constraints wildcard to fill in, if any @@ -1572,6 +1576,26 @@ if the original function had a signature like But that's ok: tcMatchesFun (called by tcRhs) can deal with that It happens, too! See Note [Polymorphic methods] in TcClassDcl. +Note [Quantified varaibles in partial type signatures] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + f :: forall a b. _ -> a -> _ -> b + f (x,y) p q = q + +Then we expect f's final type to be + f :: forall {x,y}. forall a b. (x,y) -> a -> b -> b + +Note that x,y are Inferred, and can't be use for visible type +application (VTA). But a,b are Specified, and remain Specified +in the final type, so we can use VTA for them. (Exception: if +it turns out that a's kind mentions b we need to reorder them +with scopedSort.) + +The sig_inst_skols of the TISI from a partial signature records +that original order, and is used to get the variables of f's +final type in the correct order. + + Note [Wildcards in partial signatures] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The wildcards in psig_wcs may stand for a type mentioning |