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| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2018-12-17 20:54:36 -0500 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2019-03-01 16:26:02 -0500 |
| commit | c26d299dc422f43b8c37da4b26da2067eedcbae8 (patch) | |
| tree | 517d7b87043152bee667485e186314d19b55cfba /compiler/hsSyn/HsDecls.hs | |
| parent | f838809f1e73c20bc70926fe98e735297572ac60 (diff) | |
| download | haskell-c26d299dc422f43b8c37da4b26da2067eedcbae8.tar.gz | |
Visible dependent quantification
This implements GHC proposal 35
(https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0035-forall-arrow.rst)
by adding the ability to write kinds with
visible dependent quantification (VDQ).
Most of the work for supporting VDQ was actually done _before_ this
patch. That is, GHC has been able to reason about kinds with VDQ for
some time, but it lacked the ability to let programmers directly
write these kinds in the source syntax. This patch is primarly about
exposing this ability, by:
* Changing `HsForAllTy` to add an additional field of type
`ForallVisFlag` to distinguish between invisible `forall`s (i.e,
with dots) and visible `forall`s (i.e., with arrows)
* Changing `Parser.y` accordingly
The rest of the patch mostly concerns adding validity checking to
ensure that VDQ is never used in the type of a term (as permitting
this would require full-spectrum dependent types). This is
accomplished by:
* Adding a `vdqAllowed` predicate to `TcValidity`.
* Introducing `splitLHsSigmaTyInvis`, a variant of `splitLHsSigmaTy`
that only splits invisible `forall`s. This function is used in
certain places (e.g., in instance declarations) to ensure that GHC
doesn't try to split visible `forall`s (e.g., if it tried splitting
`instance forall a -> Show (Blah a)`, then GHC would mistakenly
allow that declaration!)
This also updates Template Haskell by introducing a new `ForallVisT`
constructor to `Type`.
Fixes #16326. Also fixes #15658 by documenting this feature in the
users' guide.
Diffstat (limited to 'compiler/hsSyn/HsDecls.hs')
| -rw-r--r-- | compiler/hsSyn/HsDecls.hs | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/compiler/hsSyn/HsDecls.hs b/compiler/hsSyn/HsDecls.hs index c18a9ae1fc..f8709fbe1e 100644 --- a/compiler/hsSyn/HsDecls.hs +++ b/compiler/hsSyn/HsDecls.hs @@ -1457,7 +1457,7 @@ pprConDecl (ConDeclH98 { con_name = L _ con , con_mb_cxt = mcxt , con_args = args , con_doc = doc }) - = sep [ppr_mbDoc doc, pprHsForAll ex_tvs cxt, ppr_details args] + = sep [ppr_mbDoc doc, pprHsForAll ForallInvis ex_tvs cxt, ppr_details args] where ppr_details (InfixCon t1 t2) = hsep [ppr t1, pprInfixOcc con, ppr t2] ppr_details (PrefixCon tys) = hsep (pprPrefixOcc con @@ -1470,7 +1470,7 @@ pprConDecl (ConDeclGADT { con_names = cons, con_qvars = qvars , con_mb_cxt = mcxt, con_args = args , con_res_ty = res_ty, con_doc = doc }) = ppr_mbDoc doc <+> ppr_con_names cons <+> dcolon - <+> (sep [pprHsForAll (hsq_explicit qvars) cxt, + <+> (sep [pprHsForAll ForallInvis (hsq_explicit qvars) cxt, ppr_arrow_chain (get_args args ++ [ppr res_ty]) ]) where get_args (PrefixCon args) = map ppr args @@ -1777,7 +1777,7 @@ pprHsFamInstLHS :: (OutputableBndrId (GhcPass p)) -> LHsContext (GhcPass p) -> SDoc pprHsFamInstLHS thing bndrs typats fixity mb_ctxt - = hsep [ pprHsExplicitForAll bndrs + = hsep [ pprHsExplicitForAll ForallInvis bndrs , pprLHsContext mb_ctxt , pp_pats typats ] where |