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| author | Richard Eisenberg <eir@cis.upenn.edu> | 2016-03-19 16:55:50 -0400 |
|---|---|---|
| committer | Richard Eisenberg <eir@cis.upenn.edu> | 2016-03-21 12:16:12 -0400 |
| commit | 35e937973f61a7e5534ecd0b1c67111cd82d4238 (patch) | |
| tree | 515dd4f04763c179dad1ae1ed29ed4e5b3459bc8 /docs | |
| parent | 947709395015bd6122eedc6da5df356660e76208 (diff) | |
| download | haskell-35e937973f61a7e5534ecd0b1c67111cd82d4238.tar.gz | |
Track specified/invisible more carefully.
In particular, this allows correct tracking of specified/invisible
for variables in Haskell98 data constructors and in pattern synonyms.
GADT-syntax constructors are harder, and are left until #11721.
This was all inspired by Simon's comments to my fix for #11512,
which this subsumes.
Test case: ghci/scripts/TypeAppData
[skip ci] (The test case fails because of an unrelated problem
fixed in the next commit.)
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/glasgow_exts.rst | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/docs/users_guide/glasgow_exts.rst b/docs/users_guide/glasgow_exts.rst index 25fbb23e64..f5f266a52c 100644 --- a/docs/users_guide/glasgow_exts.rst +++ b/docs/users_guide/glasgow_exts.rst @@ -8709,6 +8709,19 @@ Here are the details: signature, ``myLength``'s inferred type will be ``forall {f} {a}. Foldable f => f a -> Int``. +- Data constructors declared with GADT syntax follow different rules + for the time being; it is expected that these will be brought in line + with other declarations in the future. The rules for GADT + data constructors are as follows: + * All kind and type variables are considered specified and available for + visible type application. + * Universal variables always come first, in precisely the order they + appear in the type delcaration. Universal variables that are + constrained by a GADT return type are not included in the data constructor. + * Existential variables come next. Their order is determined by a user- + written `forall`; or, if there is none, by taking the left-to-right order + in the data constructor's type and doing a stable topological sort. + .. _implicit-parameters: Implicit parameters |