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.