There is a weak form of modularity which can be achieved by using two parts of haskell:

1. hiding constructors in files 2. type classes

But it doesn't really begin to approach the kind of structuring that is possible in an ML-like system. Unfortunately, the issue is very (needlessly) controversial, and I don't think I want to get dragged into it here.

I'll mention, though, that Haskell does have one form of modularity which ML doesn't really, which is the fact that you can write algorithms separately, compose them together after the fact, and expect to get reasonable performance in most cases. This is because of two things: haskell is non-strict, and GHC has pretty good fusion. In ML, you often end up manually fusing things together in order to get good performance, so composition can be a bit more difficult.

> I'll mention, though, that Haskell does have one form of modularity which ML doesn't really, which is the fact that you can write algorithms separately, compose them together after the fact, and expect to get reasonable performance in most cases.

I'd actually argue the opposite. MLton is one of the best whole program optimizing compilers I have ever used. There are virtually no penalties for abstraction. OCaml has a bit of trouble here, from what I've heard, but I've never personally run into serious performance problems as a result of abstraction.

sgeisenh — wow! How cool. If that is the case, than that's awesome, and makes me very happy.