On Thu, 17 May 2007, Jason Dagit wrote:

Well, it seems to me that Haskell modules are actually very similar to singletons. Perhaps all these problems with modules having top level mutable state could be solved if Haskell modules were parameterizable at "instantiation"? I'm not saying we should turn the Haskell module system into an OO system, just that maybe it would be wise to borrow some ideas from that paradigm.

Well, I'm a little unclear as to how the discussion shifted from global variables to modules, but as long as we're here: Rather than looking at OO languages, why not take a lesson from more powerful module systems already in functional programming languages. In particular, the ML module system supports "parameterization at instantiation" with functors. Of course, there is considerable evidence that ML modules and Haskell type classes really do the same thing, but they do seem to be useful in very different situations. --Chris