[Haskell] Can we do better than duplicate APIs? [was:Data.CompactString 0.3]

[Andrzej Jaworski]

>Or maybe we have come to the point where Haskell's lack of a 'real' module
>system, like e.g. in SML, actually starts to hurt? Can associated types
>come to the rescue?

The organic growth of Haskell resulted in many compromises to the core
design. As a result Haskell inherits inadequate module system. Also all the
bells and whistles, like constraint handling rules, overlapping instances,
associated types, show that the pre-GADT type-class solutions do not allow
for too much (e.g. DoCon failure).

I believe that true dependent sums and products at the core level should
allow to capture modules at the core and be first lass. Likewise functors
should be the fundamental unit of composition at all levels. But that would
mean no back compatibility.

Cheers,
-Andrzej