Commit d8d541d8 authored by Iavor S. Diatchki's avatar Iavor S. Diatchki

Fixes (hopefully!) T9858

The changes are:
  1. No impredicative types in `Typeable`
  2. Distinguish normal tuples, from tuples of constraints.
parent 1fb4dd32
......@@ -41,10 +41,11 @@ import Digraph
import PrelNames
import TysPrim ( mkProxyPrimTy )
import TyCon ( isTupleTyCon, tyConDataCons_maybe
, tyConName, isPromotedTyCon, isPromotedDataCon )
, tyConName, isPromotedTyCon, isPromotedDataCon, tyConKind )
import TcEvidence
import TcType
import Type
import Kind (returnsConstraintKind)
import Coercion hiding (substCo)
import TysWiredIn ( eqBoxDataCon, coercibleDataCon, tupleCon, mkListTy
, mkBoxedTupleTy, stringTy )
......@@ -983,6 +984,9 @@ dsEvTypeable ev =
| isPromotedTyCon tc = appendFS (mkFastString "$k") name_fs
| isPromotedDataCon tc = appendFS (mkFastString "$c") name_fs
| isTupleTyCon tc &&
returnsConstraintKind (tyConKind tc)
= appendFS (mkFastString "$p") name_fs
| otherwise = name_fs
hashThis = unwords $ map unpackFS [pkg_fs, modl_fs, hash_name_fs]
......@@ -14,7 +14,7 @@ import TcCanonical
import TcFlatten
import VarSet
import Type
import Kind (isKind, isConstraintKind)
import Kind (isKind, isConstraintKind )
import Unify
import InstEnv( DFunInstType, lookupInstEnv, instanceDFunId )
import CoAxiom(sfInteractTop, sfInteractInert)
......@@ -1846,10 +1846,14 @@ isCallStackIP _ _ _
-- | Assumes that we've checked that this is the 'Typeable' class,
-- and it was applied to the correct argument.
matchTypeableClass :: Class -> Kind -> Type -> CtLoc -> TcS LookupInstResult
matchTypeableClass clas k t loc
matchTypeableClass clas _k t loc
-- See Note [No Typeable for qualified types]
| isForAllTy t = return NoInstance
| isConstraintKind k = return NoInstance
-- See Note [No Typeable for qualified types]
-- Is the type of the form `C => t`?
| Just (t1,_) <- splitFunTy_maybe t,
isConstraintKind (typeKind t1) = return NoInstance
| Just (tc, ks) <- splitTyConApp_maybe t
, all isKind ks = doTyCon tc ks
| Just (f,kt) <- splitAppTy_maybe t = doTyApp f kt
......@@ -1902,8 +1906,6 @@ matchTypeableClass clas k t loc
We do not support impredicative typeable, such as
Typeable (forall a. a->a)
Typeable (Eq a => a -> a)
Typeable (Eq a)
Typeable (() :: Constraint)
Typeable (() => Int)
Typeable (((),()) => Int)
......@@ -1914,19 +1916,9 @@ a TypeRep for them. For qualified but not polymorphic types, like
* We don't need a TypeRep for these things. TypeReps are for
monotypes only.
* The types (Eq a, Show a) => ...blah...
and Eq a => Show a => ...blah...
are represented the same way, as a curried function;
that is, the tuple before the '=>' is just syntactic
sugar. But since we can abstract over tuples of constraints,
we really do have tuples of constraints as well.
This dichotomy is not well worked out, and Trac #9858 comment:76
shows that Typeable treated it one way, while newtype instance
matching treated it another. Or maybe it was the fact that
'*' and Constraint are distinct to the type checker, but are
the same afterwards. Anyway, the result was a function of
type (forall ab. a -> b), which is pretty dire.
So the simple solution is not to attempt Typable for constraints.
* Perhaps we could treat `=>` as another type constructor for `Typeable`
purposes, and thus support things like `Eq Int => Int`, however,
at the current state of affairs this would be an odd exception as
no other class works with impredicative types.
For now we leave it off, until we have a better story for impredicativity.
{-# LANGUAGE ImpredicativeTypes #-}
{-# LANGUAGE FlexibleContexts #-}
module T9858b where
import Data.Typeable
test = typeRep (Proxy :: Proxy (Eq Int => Int))
T9858b.hs:7:8: error:
No instance for (Typeable (Eq Int => Int))
(maybe you haven't applied a function to enough arguments?)
arising from a use of ‘typeRep’
In the expression: typeRep (Proxy :: Proxy (Eq Int => Int))
In an equation for ‘test’:
test = typeRep (Proxy :: Proxy (Eq Int => Int))
......@@ -357,3 +357,4 @@ test('T9999', normal, compile_fail, [''])
test('T10194', normal, compile_fail, [''])
test('T8030', normal, compile_fail, [''])
test('T9858a', normal, compile_fail, [''])
test('T9858b', normal, compile_fail, [''])
{-# LANGUAGE KindSignatures #-}
module Main(main) where
import Data.Typeable
import GHC.Exts
test1 :: Bool
test1 = typeRep (Proxy :: Proxy (() :: *)) ==
typeRep (Proxy :: Proxy (() :: Constraint))
test2 :: Bool
test2 = typeRepTyCon (typeRep (Proxy :: Proxy (Int,Int))) ==
typeRepTyCon (typeRep (Proxy :: Proxy (Eq Int, Eq Int)))
main :: IO ()
main = print (test1,test2)
......@@ -117,3 +117,4 @@ test('T9497a-run', [exit_code(1)], compile_and_run, ['-fdefer-typed-holes'])
test('T9497b-run', [exit_code(1)], compile_and_run, ['-fdefer-typed-holes -fno-warn-typed-holes'])
test('T9497c-run', [exit_code(1)], compile_and_run, ['-fdefer-type-errors -fno-warn-typed-holes'])
test('T9858b', normal, compile_and_run, [''])
test('T9858c', normal, compile_and_run, [''])
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