Binary: Put -> Builder

[Ross Paterson]

On Thu, Feb 12, 2009 at 07:28:07AM -0800, Don Stewart wrote:
> ross:
> > Here's a concrete suggestion: have Data.Binary.Put export the existing
> > function
> > 
> >   tell :: Builder -> Put
> > 
> > and also
> > 
> >   execPut :: PutM a -> Builder
> >   execPut = sndS . unPut
> 
> What's the use case?

Quoting a previous message:
> I imagine one might want to make a Builder for a composite object,
> using the Binary instances of some types.  And one might want to go
> the other way too, defining a Binary instance using an existing Builder.