Ross Paterson <[EMAIL PROTECTED]> wrote:
> > Thu Aug 31 03:11:05 PDT 2006 [EMAIL PROTECTED]
> > * import Control.Arrow.ArrowZero to help nhc98's type checker
> >
> > M ./Data/Foldable.hs +1
>
> That's an unusual, um, feature. The module doesn't use arrows at all,
> but it uses a class, one of whose instances (defined elsewhere) uses
> ArrowZero.
That could be the cause. The error I was seeing from nhc98 was a
dependency problem, essentially that something in Data.Foldable needed
(indirectly) the class ArrowZero, but the class had not been imported
earlier, because a different dependency analysis had not realised the
need.
> Does this happen a lot?
Occasionally. Not often I would say. It certainly indicates a bug in
nhc98, but having searched for these things before, it is often cheaper
to work around it than to find it.
Regards,
Malcolm
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