diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/typecheck/TcRnDriver.hs | 44 | ||||
| -rw-r--r-- | compiler/types/TypeRep.hs | 2 |
2 files changed, 32 insertions, 14 deletions
diff --git a/compiler/typecheck/TcRnDriver.hs b/compiler/typecheck/TcRnDriver.hs index 2ac45fc224..1fb7662b59 100644 --- a/compiler/typecheck/TcRnDriver.hs +++ b/compiler/typecheck/TcRnDriver.hs @@ -1743,7 +1743,7 @@ tcRnExpr hsc_env rdr_expr (rn_expr, _fvs) <- rnLExpr rdr_expr ; failIfErrsM ; - -- Now typecheck the expression; + -- Now typecheck the expression, and generalise its type -- it might have a rank-2 type (e.g. :t runST) uniq <- newUnique ; let { fresh_it = itName uniq (getLoc rdr_expr) } ; @@ -1755,7 +1755,7 @@ tcRnExpr hsc_env rdr_expr False {- No MR for now -} [(fresh_it, res_ty)] lie ; - -- wanted constraints from static forms + -- Wanted constraints from static forms stWC <- tcg_static_wc <$> getGblEnv >>= readTcRef ; -- Ignore the dictionary bindings @@ -1797,7 +1797,13 @@ tcRnType hsc_env normalise rdr_type -- Now kind-check the type -- It can have any rank or kind ; nwc_tvs <- mapM newWildcardVarMetaKind wcs - ; ty <- tcExtendTyVarEnv nwc_tvs $ tcHsSigType GhciCtxt rn_type + ; (ty, kind) <- tcExtendTyVarEnv nwc_tvs $ + tcLHsType rn_type + + -- Do kind generalisation; see Note [Kind-generalise in tcRnType] + ; kvs <- zonkTcTypeAndFV kind + ; kvs <- kindGeneralize kvs + ; ty <- zonkTcTypeToType emptyZonkEnv ty ; ty' <- if normalise then do { fam_envs <- tcGetFamInstEnvs @@ -1806,20 +1812,32 @@ tcRnType hsc_env normalise rdr_type -- which we discard, so the Role is irrelevant else return ty ; - ; return (ty', typeKind ty) } + ; return (ty', mkForAllTys kvs (typeKind ty')) } -{- -Note [Kind-generalise in tcRnType] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +{- Note [Kind-generalise in tcRnType] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We switch on PolyKinds when kind-checking a user type, so that we will -kind-generalise the type. This gives the right default behaviour at -the GHCi prompt, where if you say ":k T", and T has a polymorphic -kind, you'd like to see that polymorphism. Of course. If T isn't -kind-polymorphic you won't get anything unexpected, but the apparent -*loss* of polymorphism, for types that you know are polymorphic, is -quite surprising. See Trac #7688 for a discussion. +kind-generalise the type, even when PolyKinds is not otherwise on. +This gives the right default behaviour at the GHCi prompt, where if +you say ":k T", and T has a polymorphic kind, you'd like to see that +polymorphism. Of course. If T isn't kind-polymorphic you won't get +anything unexpected, but the apparent *loss* of polymorphism, for +types that you know are polymorphic, is quite surprising. See Trac +#7688 for a discussion. + +Note that the goal is to generalise the *kind of the type*, not +the type itself! Example: + ghci> data T m a = MkT (m a) -- T :: forall . (k -> *) -> k -> * + ghci> :k T +We instantiate T to get (T kappa). We do not want to kind-generalise +that to forall k. T k! Rather we want to take its kind + T kappa :: (kappa -> *) -> kappa -> * +and now kind-generalise that kind, to forall k. (k->*) -> k -> * +(It was Trac #10122 that made me realise how wrong the previous +approach was.) -} +{- ************************************************************************ * * tcRnDeclsi diff --git a/compiler/types/TypeRep.hs b/compiler/types/TypeRep.hs index 77e998d490..c78c9c5975 100644 --- a/compiler/types/TypeRep.hs +++ b/compiler/types/TypeRep.hs @@ -639,7 +639,7 @@ pprSigmaTypeExtraCts :: Bool -> Type -> SDoc pprSigmaTypeExtraCts = ppr_sigma_type False pprUserForAll :: [TyVar] -> SDoc --- Print a user-level forall; see Note [WHen to print foralls] +-- Print a user-level forall; see Note [When to print foralls] pprUserForAll tvs = sdocWithDynFlags $ \dflags -> ppWhen (any tv_has_kind_var tvs || gopt Opt_PrintExplicitForalls dflags) $ |