G'day all.
One small note on style while I think of it.
Quoting Derek Elkins
module FooInternals where
publicFoo :: Foo -> Bar publicFoo x = privateFrob x
privateFrob x :: Foo -> Bar privateFrob x = ...
debugFoo :: (Foo -> Bar) -> Foo -> Bar debugFoo f x = ...
module Foo ( publicFoo ) where import FooInternals
module FooDebug ( publicFoo, debugFoo ) where import FooInternals
I would put debugFoo in FooDebug, and not export publicFoo. The former is an advantage because unit test code doesn't end up in the executable, and the latter is an advantage because it turns a triple maintenance problem into a double maintenance problem. (Should you add a new public function to FooInternals, you only have to mention it in Foo and not in FooDebug as well.) The reason why this is inelegant is that in Haskell, the unit of abstraction (i.e. the module) is the same as the unit of compilation (i.e. the file). If there are some budding researchers who are looking for a topic, I'd love a way to split a module across files without the situation degenerating into C-style textual inclusion. Cheers, Andrew Bromage