Mutually recursive modules and derived instances of Data

Martin Sjögren msjogren at
Wed Oct 13 08:57:49 EDT 2004

On Wed, 13 Oct 2004 13:21:26 +0100, Simon Peyton-Jones
<simonpj at> wrote:
> 1.  Separate 'deriving' from the data type decl, so you can say
>         derive( Data TA, Typeable TA )
> anywhere.  People sometimes ask for this for other reasons.
> 2.  Allow instances in hi-boot files
> You might say "both would be useful", but I'd be interested in people's
> opinions about which of (1) or (2) would be preferable if you could only
> have one or t'other.

1! As you say, people sometimes ask for this for other reasons. I'm
one of them, though I'm not sure if I've actually asked about it on
the list. Separating deriving from the declaration would be incredibly


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