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| author | sheaf <sam.derbyshire@gmail.com> | 2021-10-15 23:09:39 +0200 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2021-10-17 14:06:46 -0400 |
| commit | 81740ce83976e9d6b68594f8a4b489452cca56e5 (patch) | |
| tree | 7b41d1529975c2f78eaced81e26e4722d34c212f /docs | |
| parent | 65bf3992aebb3c08f0c4e13a3fb89dd5620015a9 (diff) | |
| download | haskell-81740ce83976e9d6b68594f8a4b489452cca56e5.tar.gz | |
Introduce Concrete# for representation polymorphism checks
PHASE 1: we never rewrite Concrete# evidence.
This patch migrates all the representation polymorphism checks to
the typechecker, using a new constraint form
Concrete# :: forall k. k -> TupleRep '[]
Whenever a type `ty` must be representation-polymorphic
(e.g. it is the type of an argument to a function), we emit a new
`Concrete# ty` Wanted constraint. If this constraint goes
unsolved, we report a representation-polymorphism error to the user.
The 'FRROrigin' datatype keeps track of the context of the
representation-polymorphism check, for more informative error messages.
This paves the way for further improvements, such as
allowing type families in RuntimeReps and improving the soundness
of typed Template Haskell. This is left as future work (PHASE 2).
fixes #17907 #20277 #20330 #20423 #20426
updates haddock submodule
-------------------------
Metric Decrease:
T5642
-------------------------
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/9.4.1-notes.rst | 3 | ||||
| -rw-r--r-- | docs/users_guide/exts/defer_type_errors.rst | 7 |
2 files changed, 9 insertions, 1 deletions
diff --git a/docs/users_guide/9.4.1-notes.rst b/docs/users_guide/9.4.1-notes.rst index ce70b8e98d..0e776672eb 100644 --- a/docs/users_guide/9.4.1-notes.rst +++ b/docs/users_guide/9.4.1-notes.rst @@ -13,6 +13,9 @@ Compiler defaults for ambiguous variables that would otherwise cause errors just like the built-in defaulting mechanism. +- The way GHC checks for representation polymorphism has been overhauled: + all the checks are now done during typechecking. The error messages + now contain more detailed information about the specific check that was performed. ``base`` library ~~~~~~~~~~~~~~~~ diff --git a/docs/users_guide/exts/defer_type_errors.rst b/docs/users_guide/exts/defer_type_errors.rst index c9e4accb13..8d502d3708 100644 --- a/docs/users_guide/exts/defer_type_errors.rst +++ b/docs/users_guide/exts/defer_type_errors.rst @@ -107,7 +107,7 @@ example, an ill-kinded type signature, an instance declaration that is non-terminating or ill-formed, a type-family instance that does not obey the declared injectivity constraints, etc etc. -In a few cases, equality constraints cannot be deferred. Specifically: +In a few cases, some constraints cannot be deferred. Specifically: - Kind errors in a type or kind signature, partial type signatures, or pattern signature. e.g. :: @@ -130,3 +130,8 @@ In a few cases, equality constraints cannot be deferred. Specifically: f :: a %1 -> a f _ = () + +- Illegal representation polymorphism, e.g. :: + + f :: forall rep (a :: TYPE rep). a -> a + f a = a |