[Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)

[Alfonso Acosta]

On Feb 7, 2008 9:01 PM, Dan Weston <westondan at imageworks.com> wrote:
> This may be a GHC bug, but even though in the module
> Data.TypeLevel.Num.Reps has the header
>
> {-# LANGUAGE EmptyDataDecls, TypeOperators #-}
>
> I still get an error with both ghc and ghci version 6.8.2 unless I throw
> in the -XTypeOperators flag.

If you are using type operators in a module you have to supply the
flag, independently of what flags are supplied in other modules.

The same applies for other extensions which modify the _syntax_ of the
language (e.g. Template Haskell etc ...)

So, it's not a bug.

As a side note, even if the TypeOperators flag is supplied GHC 6.8.2
fires an error with the following declaration:

instance (Compare x y CEQ) => x :==: y -- GHC fires a "Malformed
instance header" error

whereas using an equivalent prefix definition works just fine

instance (Compare x y CEQ) => (:==:) x y