[Haskell-cafe] instance Binary UTCTime

Ivan Lazar Miljenovic ivan.miljenovic at gmail.com
Sun Nov 29 22:56:20 EST 2009

Alexander Dunlap <alexander.dunlap at gmail.com> writes:
> Well, that happens anyway with most packages since distros have to
> choose one set of flags that works. The proposal I was commenting on
> would just allow packages to depend on flags of other packages and so
> be explicit about this.

Consider this problem:

* Package Foo has an optional instance, enabled with the --foo flag.

* Package Bar wants that instance.

* Package Baz doesn't want that instance, since it uses its own custom
  instance (e.g. yi's instance of Category for Data.Accessor.Basic.T,
  which clashes with the one added to data-accessor 0.2.1).

* You want to install both Bar and Baz.

Which one do you end up using?  You can't have the same version of Foo
installed twice (as far as I know anyway).

It would be nice to have a separate namespace in exports/imports for
instances so you _can_ selectively override them if you so wish, but
that will probably cause other problems.

Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com

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