Re: packages with orphaned instances only

On 7 January 2011 23:07, Stephen Tetley wrote:

On 7 January 2011 10:22, Christian Maeder wrote:

...

So is this a bad idea?

It sounds like a good idea to me.

There might be some details to trash out, e.g. the granularity of packages - should there be a Quickcheck-orphans with Arbitrary instances for many structures, or separate packages (quickcheck-containers-instances, quickcheck-array-instances, ...) and perhaps a new top-level Hackage category is needed so people know where to find them - "Canonical instances", "Orphan instances", ...?

My biggest problem with "official" instances such as these is that they may not do what you want. For example, I have a lot of problems with the testsuite for graphviz because the default list (and hence String) instances do not match the behaviour required, so I have to be careful to make sure I use my custom arbString, etc. functions rather than directly calling arbitrary. That said, if these packages have one-instance-per-module (as in separate modules defining the Arbitrary instances for Map, Set, etc.) then this situation is greatly reduced, since if I want a custom Map instance I just have to make sure I don't import the module that provides the default one. -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com