[Haskell-cafe] Named function fields vs. type classes

[John Goerzen]

Hi,

I often have a situation where I'm designing specialized components to
do a more general task.   Examples could include mail folder code (maildir,
mbox, etc), configuration file parsing, protocol handlers for URL
accesses, logging backends, etc.

For some of these, I've used a data object with named fields, each one
of them being a function that performs various tasks (open connection to
the URL, read data, whatever.)  So, I get a standard interface.  The
advantage of this approach is that I can build a list containing all
sorts of different data objects in it.

For others, I've used typeclasses, and made the different specialized
components a member of the typeclass.  This seems to provide a cleaner
interface, and one that is more readily extended (maybe I want to
support IMAP folders, and support all its searching capabilities too).

On the other hand, it's difficult or impossible to make a list of a
bunch of different types of things that have nothing in common save
being members of the class.

Is there any advice on the best way to do these things?

Thanks,

John