On 27/05/2009 22:02, Henning Thielemann wrote:
My proposal is thus: Discourage orphan instances! If you encounter that
an instance is missing and it is a canonical one, it should be added to
the package that defines the type or the class. If there are several
choices for the implementation then the package where the instance would
belong to should document that. Then programmers should find a consensus
which of the choices they prefer. If you cannot wait for an official
adaption of the required instance, then you must work with newtype
wrappers.
Quite. I argued the "no orphan instances in libraries" position on the
libraries list last year, here's the start of the (longish) thread:
http://www.haskell.org/pipermail/libraries/2008-September/010618.html
We ought to have a "guidelines for API design" section of the wiki
somewhere, so we could put this in it.
Cheers,
Simon
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