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author | Ryan Scott <ryan.gl.scott@gmail.com> | 2020-10-24 10:39:50 -0400 |
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committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-10-30 18:52:50 -0400 |
commit | 31fcb55f4ff8c06c5ab100a6817cae8b571295a9 (patch) | |
tree | d7c46a6e6b9f0f7bdf807f7e6e27d2d593e83251 /compiler/GHC/Tc/Utils/TcType.hs | |
parent | 9902d9ec95dfc3ddb3e8a703de6b000c3ac3871a (diff) | |
download | haskell-31fcb55f4ff8c06c5ab100a6817cae8b571295a9.tar.gz |
Split HsConDecl{H98,GADT}Details
Haskell98 and GADT constructors both use `HsConDeclDetails`, which includes
`InfixCon`. But `InfixCon` is never used for GADT constructors, which results
in an awkward unrepresentable state. This removes the unrepresentable state by:
* Renaming the existing `HsConDeclDetails` synonym to `HsConDeclH98Details`,
which emphasizes the fact that it is now only used for Haskell98-style data
constructors, and
* Creating a new `HsConDeclGADTDetails` data type with `PrefixConGADT` and
`RecConGADT` constructors that closely resemble `PrefixCon` and `InfixCon`
in `HsConDeclH98Details`. The key difference is that `HsConDeclGADTDetails`
lacks any way to represent infix constructors.
The rest of the patch is refactoring to accommodate the new structure of
`HsConDecl{H98,GADT}Details`. Some highlights:
* The `getConArgs` and `hsConDeclArgTys` functions have been removed, as
there is no way to implement these functions uniformly for all
`ConDecl`s. For the most part, their previous call sites now
pattern match on the `ConDecl`s directly and do different things for
`ConDeclH98`s and `ConDeclGADT`s.
I did introduce one new function to make the transition easier:
`getRecConArgs_maybe`, which extracts the arguments from a `RecCon(GADT)`.
This is still possible since `RecCon(GADT)`s still use the same representation
in both `HsConDeclH98Details` and `HsConDeclGADTDetails`, and since the
pattern that `getRecConArgs_maybe` implements is used in several places,
I thought it worthwhile to factor it out into its own function.
* Previously, the `con_args` fields in `ConDeclH98` and `ConDeclGADT` were
both of type `HsConDeclDetails`. Now, the former is of type
`HsConDeclH98Details`, and the latter is of type `HsConDeclGADTDetails`,
which are distinct types. As a result, I had to rename the `con_args` field
in `ConDeclGADT` to `con_g_args` to make it typecheck.
A consequence of all this is that the `con_args` field is now partial, so
using `con_args` as a top-level field selector is dangerous. (Indeed, Haddock
was using `con_args` at the top-level, which caused it to crash at runtime
before I noticed what was wrong!) I decided to add a disclaimer in the 9.2.1
release notes to advertise this pitfall.
Fixes #18844. Bumps the `haddock` submodule.
Diffstat (limited to 'compiler/GHC/Tc/Utils/TcType.hs')
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