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| author | simonpj@microsoft.com <unknown> | 2009-10-30 09:59:29 +0000 |
|---|---|---|
| committer | simonpj@microsoft.com <unknown> | 2009-10-30 09:59:29 +0000 |
| commit | af28015f9139151ef33098481e774be92bfcbe8f (patch) | |
| tree | 9ffe358c4fd37d3543c2098b800345c668bc3fe6 /compiler | |
| parent | 0600645a1f0a4ebb7861038ccf6d0ffcfbbadcad (diff) | |
| download | haskell-af28015f9139151ef33098481e774be92bfcbe8f.tar.gz | |
Deprecate the ImpredicativeTypes feature
GHC has had an experimental implementation of impredicative
polymorphism for a year or two now (flag -XImpredicativeTypes).
But
a) The implementation is ridiculously complicated, and the complexity
is pervasive (in the type checker) rather than localized.
I'm very unhappy about this, especially as we add more stuff to
the type checker for type families.
b) The specification (type system) is well-defined [1], but is also pretty
complicated, and it's just too hard to predict which programs will
typecheck and which will not.
So it's time for a re-think. I propose to deprecate it in 6.12, and
remove it altogether in 6.14. We may by then have something else to
put in its place. (There is no lack of candidates [2,3,4]!)
[1] http://research.microsoft.com/en-us/um/people/simonpj/papers/boxy/
[2] http://research.microsoft.com/en-us/um/people/crusso/qml/
[3] http://research.microsoft.com/en-us/um/people/daan/pubs.html
[4] http://gallium.inria.fr/~remy/mlf/
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/main/DynFlags.hs | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/compiler/main/DynFlags.hs b/compiler/main/DynFlags.hs index d445055197..e5a549af6b 100644 --- a/compiler/main/DynFlags.hs +++ b/compiler/main/DynFlags.hs @@ -1811,7 +1811,8 @@ xFlags = [ ( "LiberalTypeSynonyms", Opt_LiberalTypeSynonyms, const Supported ), ( "Rank2Types", Opt_Rank2Types, const Supported ), ( "RankNTypes", Opt_RankNTypes, const Supported ), - ( "ImpredicativeTypes", Opt_ImpredicativeTypes, const Supported ), + ( "ImpredicativeTypes", Opt_ImpredicativeTypes, + const $ Deprecated "Impredicative polymorphism will be simplified or removed in GHC 6.14" ), ( "TypeOperators", Opt_TypeOperators, const Supported ), ( "RecursiveDo", Opt_RecursiveDo, deprecatedForLanguage "DoRec"), |