#4235: deriving Enum fails for data instances
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Reporter: nestra | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 6.14.1
Component: Compiler (Type checker) | Version: 6.12.3
Keywords: instance deriving, type families, GADTs | Testcase:
Blockedby: | Difficulty:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure:
Compile-time performance bug
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Comment(by nestra):
I discovered that this bug occurs even with the following example:
{{{
module Foo where
data Foo a
= A | B
deriving (Enum)
}}}
{{{
Foo.hs:1:0:
Expecting an ordinary type, but found a type of kind * -> *
In an expression type signature: Foo
In the expression: GHC.Prim.tagToEnum# a :: Foo
In the definition of `Foo.$tag2con_Foo':
Foo.$tag2con_Foo (GHC.Types.I# a) = GHC.Prim.tagToEnum# a :: Foo
}}}
So, the bug is not specific to the extensions (although the examples
revealing it occur in practice more probably when programming with type
families or GADTs).
The same behaviour is observed in the case of deriving Ix.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4235#comment:2>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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