Thanks for pointing me at Iavors package. We should not have two different libraries for the same purpose. value-supply-0.2 is about 6-7 times slower than GHC's UniqSupply, but porting Simons suggestion (to use unsafeDupableInterleaveIO) into Iavors code, GHC is "only" about twice as fast. Can we do better? I tried to use SPECIALIZE INLINE pragmas (at new[Enum|Num]Supply for Int) and/or strictness annotations (for the unique value) without significant benefit. I like Iavors more general interface (polymorphic values) and that only demanded identifiers are created. The latter saves half of the names when evaluating
map supplyValue . split
I will replace my dependency to ghc with one to value-supply if unsafeDupableInterleaveIO is used instead of unsafeInterleaveIO where it is available. Cheers, Sebastian