#3830: weird error message from type qualification mistake
------------------------------------------------+---------------------------
Reporter: guest | Owner:
Type: bug | Status: closed
Priority: normal | Milestone:
Component: Compiler | Version: 6.10.4
Resolution: fixed | Keywords:
Difficulty: | Os: Linux
Testcase: | Architecture: x86_64
(amd64)
Failure: Incorrect warning at compile-time |
------------------------------------------------+---------------------------
Changes (by simonpj):
* status: new => closed
* resolution: => fixed
Old description:
> {-# LANGUAGE GADTs, RankNTypes #-}
>
> data Parity a where
> Odd :: Int -> forall a. Parity (Int,Int,a)
>
> (the "forall a" is in the wrong place) gives the error message
>
> Malformed constructor result type:
> forall a :: k_a3Gz. Parity (Int, Int, a)
>
> That k_a3Gz. is a little bit cryptic.
>
> --solrize
New description:
{{{
{-# LANGUAGE GADTs, RankNTypes #-}
data Parity a where
Odd :: Int -> forall a. Parity (Int,Int,a)
}}}
(the "forall a" is in the wrong place) gives the error message
{{{
Malformed constructor result type:
forall a :: k_a3Gz. Parity (Int, Int, a)
}}}
That k_a3Gz. is a little bit cryptic.
--solrize
--
Comment:
Good point. The message from 6.12 is better
{{{
T3830.hs:4:3:
Data constructor `Odd' returns type `forall a.
Parity (Int, Int, a)'
instead of an instance of its parent type `Parity a'
In the definition of data constructor `Odd'
In the data type declaration for `Parity'
}}}
Nevertheless, I also added a little more info to `HsTyVarBndr` to prevent
this kind of thing happening again.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3830#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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