Adding binary to the Haskell Platform

Don Stewart dons at
Wed Aug 5 16:47:07 EDT 2009

> On Wed, Aug 5, 2009 at 1:34 PM, Don Stewart<dons at> wrote:
> > alexander.dunlap:
> >> To add to the laundry list of problems with Data.Binary, I don't like
> >> the fact that decode calls error on invalid input. I can't think of
> >> any great alternatives (using Maybe as the result type would be too
> >> strict, of course, and returning partial results would be difficult
> >> with polymorphism), but it seems a bit unclean that decode has to be
> >> used with the IO monad to catch the errors. (Of course, the only
> >> reason you would have bad input would be if you were using the IO
> >> monad, so the practical implications are not great, but still, it
> >> would be nice if there was a better way.)
> >
> > That's right. Originally, it used a custom Either type, but it isn't
> > possible to stream decoders that way.
> >
> > I'd consider it an intentional design feature.
> >
> > -- Don
> >
> OK. Would it be worth creating an extensible exception (something like
> BinaryDecodeError) for this then, instead of using the call to error?
> That would at least make it less error-prone to catch.

I think that would be a good idea. Showing how to catch it in the

I'm wary of breaking the 70 packages that use Data.Binary for this,
rather, add this as a list of API changes for the next major release.

-- Don

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