I've created a wiki page to track the common errors when upgrading to
GHC 7.
http://haskell.org/haskellwiki/Upgrading_packages/Updating_to_GHC_7
Solutions to each problem should be listed here.
simonpj:
> I've been meaning to write a blog post about this, because it's a
> significant change. I'll do this when I get home after ICFP. Briefly though:
>
> * If you use -XGADTs or -XTypeFamilies (or -fglasgow-exts, which is
> deprecated) you get -XMonoLocalBinds, which says that local let/where
> bindings are not auto-generalised. There's an extensive discussion of the
> reason for this decision in our paper "Let should not be generalised" and the
> journal version http://haskell.org/haskellwiki/Simonpj/Talk:OutsideIn
>
> * One of the main times this matters is in situations like
> foo = runST (bar 5)
> where bar x = return x
> Here 'bar' must have a polymorphic type, in order to be mentioned in runST's
> argument
>
> * The error message does point out that 'bar' is a possible culprit. In
> David's example:
> The following variables have types that mention s
> fill0 :: MBUArr s e -> ST s Int
>
> * The solution is usually to add a type signature for the offending variable
> (fillO in this case); you can still have polymorphic bindings in let/where,
> but they need a type signature.
>
> Simon
>
> | -----Original Message-----
> | From: [email protected]
> [mailto:glasgow-haskell-users-
> | [email protected]] On Behalf Of David Fox
> | Sent: 29 September 2010 04:11
> | To: [email protected]
> | Subject: Re: ANNOUNCE: GHC 7.0.1 Release Candidate 1
> |
> | I'm seeing errors like this in various places, which I guess are
> | coming from the new type checker:
> |
> | Data/Array/Vector/Prim/BUArr.hs:663:3:
> | Couldn't match type `s' with `s3'
> | because this skolem type variable would escape: `s3'
> | This skolem is bound by the polymorphic type `forall s. ST s a'
> | The following variables have types that mention s
> | fill0 :: MBUArr s e -> ST s Int
> | (bound at Data/Array/Vector/Prim/BUArr.hs:669:5)
> | In the first argument of `runST', namely
> | `(do { marr <- newMBU n;
> | n' <- fill0 marr;
> | unsafeFreezeMBU marr n' })'
> |
> | I would love to hear an explanation about what they mean and what to
> | do about them. (This one is from uvector.)
> | _______________________________________________
> | Glasgow-haskell-users mailing list
> | [email protected]
> | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>
> _______________________________________________
> Glasgow-haskell-users mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
_______________________________________________
Glasgow-haskell-users mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
