Many thanks for Data.HashTable, which I am about to use. Unfortunately I seem to need an unseemly hack because the key I want, namely ThreadId's, don't have a hash function defined, and defining one requires me to muck around with GHC internal functions. Could some more hash functions be provided?
The logical method would be to have
class HashKey key where hash :: key -> Int32
and define it for as many types as possible.
I think the reason I didn't do this was because the choice of a hash function usually depends on more than just the type of the data you want to hash. For example, there are lots of hash functions over Int, but you'll want to pick one that works well for the distribution of values you have. There really ought to be a way to get an Int from a ThreadId, though. Cheers, Simon