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| author | Ryan Scott <ryan.gl.scott@gmail.com> | 2020-07-05 16:15:01 -0400 |
|---|---|---|
| committer | Ryan Scott <ryan.gl.scott@gmail.com> | 2020-10-30 19:38:31 -0400 |
| commit | e9b2578fa17989f13ec6ba8fae0c35b2dac4d900 (patch) | |
| tree | 2032245a504f20b62c0980cd84208673f45c2ac4 /compiler/GHC/Tc/Utils/Monad.hs | |
| parent | 31fcb55f4ff8c06c5ab100a6817cae8b571295a9 (diff) | |
| download | haskell-wip/T16762.tar.gz | |
Replace HsImplicitBndrs with HsOuterTyVarBndrswip/T16762
This refactors the GHC AST to remove `HsImplicitBndrs` and replace it with
`HsOuterTyVarBndrs`, a type which records whether the outermost quantification
in a type is explicit (i.e., with an outermost, invisible `forall`) or
implicit. As a result of this refactoring, it is now evident in the AST where
the `forall`-or-nothing rule applies: it's all the places that use
`HsOuterTyVarBndrs`. See the revamped `Note [forall-or-nothing rule]` in
`GHC.Hs.Type` (previously in `GHC.Rename.HsType`).
Moreover, the places where `ScopedTypeVariables` brings lexically scoped type
variables into scope are a subset of the places that adhere to the
`forall`-or-nothing rule, so this also makes places that interact with
`ScopedTypeVariables` easier to find. See the revamped
`Note [Lexically scoped type variables]` in `GHC.Hs.Type` (previously in
`GHC.Tc.Gen.Sig`).
`HsOuterTyVarBndrs` are used in type signatures (see `HsOuterSigTyVarBndrs`)
and type family equations (see `HsOuterFamEqnTyVarBndrs`). The main difference
between the former and the latter is that the former cares about specificity
but the latter does not.
There are a number of knock-on consequences:
* There is now a dedicated `HsSigType` type, which is the combination of
`HsOuterSigTyVarBndrs` and `HsType`. `LHsSigType` is now an alias for an
`XRec` of `HsSigType`.
* Working out the details led us to a substantial refactoring of
the handling of explicit (user-written) and implicit type-variable
bindings in `GHC.Tc.Gen.HsType`.
Instead of a confusing family of higher order functions, we now
have a local data type, `SkolemInfo`, that controls how these
binders are kind-checked.
It remains very fiddly, not fully satisfying. But it's better
than it was.
Fixes #16762. Bumps the Haddock submodule.
Co-authored-by: Simon Peyton Jones <simonpj@microsoft.com>
Co-authored-by: Richard Eisenberg <rae@richarde.dev>
Co-authored-by: Zubin Duggal <zubin@cmi.ac.in>
Diffstat (limited to 'compiler/GHC/Tc/Utils/Monad.hs')
| -rw-r--r-- | compiler/GHC/Tc/Utils/Monad.hs | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/compiler/GHC/Tc/Utils/Monad.hs b/compiler/GHC/Tc/Utils/Monad.hs index e42fe42799..0ff826bb96 100644 --- a/compiler/GHC/Tc/Utils/Monad.hs +++ b/compiler/GHC/Tc/Utils/Monad.hs @@ -1845,8 +1845,8 @@ It's distressingly delicate though: the visible type application fails in the monad (throws an exception). We must not discard the out-of-scope error. - Also GHC.Tc.Solver.emitFlatConstraints may fail having emitted some - constraints with skolem-escape problems. + Also GHC.Tc.Solver.simplifyAndEmitFlatConstraints may fail having + emitted some constraints with skolem-escape problems. * If we discard too /few/ constraints, we may get the misleading class constraints mentioned above. But we may /also/ end up taking |