The base library and GHC 6.10

José Pedro Magalhães jpm at
Thu Aug 28 07:25:25 EDT 2008


On Thu, Aug 28, 2008 at 13:12, Ian Lynagh <igloo at> wrote:

> First the easy bit: The Data.Generics hierarchy is going to have a
> separate maintainer, and I think that everyone is agreed that it should
> be pulled out into an "syb package". I'll treat this as not part of base
> from here on.
> The only thing still being debated here is whether the Data class itself
> should remain in base or not. Some people believe that it should remain
> in base, as it is desirable to have Data instances for as many types as
> possible, and because there is a resistance among library writers
> against adding dependencies. The counter argument is that there are many
> other classes that the same is true of (e.g. uniplate, syb-with-class,
> binary), and it does not scale to put all of these classes into base.
> Also, by requiring a dep to be added even for the classes that have
> historically been included in base, adding dependencies for the sake of
> providing instances may become more socially acceptable.

Is there a way not to have the Data class in base while still preserving the
deriving mechanism? I think that one big reason for the popularity of SYB is
not only the fact that it comes with GHC but also that you get support for
generics on user-defined datatypes for "free". So if there is no way to have
derivable Data with Data outside base, then I think Data should stay in

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