On Mon, Jan 28, 2013 at 5:43 PM, Bob Hutchison <hutch-lists@recursive.ca> wrote:

Now, this is how I got caught: it seems to be impossible to have collections of things with a common type class if they have different types. How is it that I've written that many lines of code in Haskell and I'm just noticing this now? (If I wasn't so annoyed, I'd look for something clever to reflect how loc count obviously doesn't mean much… but clever seems to be beyond me today).

Is this true? Are there any GHC extensions that will let me around this?

I just encountered this recently myself. There is a GADT extension [1][2] that may help. The greater abstraction appears to lie in existential types [3].

That being said, I'm a beginner as well and haven't yet used these extensions. So far I have found that my code is simplified by redefining heterogeneous types in terms of homogeneous functions.  If I have a class that implements common methods, I will reorganize lists by common function types rather than by class.

Cheers,
Darren


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[1] http://www.haskell.org/haskellwiki/GADT
[2] http://www.haskell.org/haskellwiki/GADTs_for_dummies
[3] http://www.haskell.org/haskellwiki/Existential_type