Memoize a Double function in Haskell

Question

I have a function

slow :: Double -> Double

which gets called very often (hundreds of millions of times), but only gets called on about a thousand discrete values. This seems like an excellent candidate for memoization, but I can't figure out how to memoize a function of a Double.

The standard technique of making a list doesn't work, since it's not an integral type. I looked at Data.MemoCombinators, but it doesn't natively support Doubles. There was a bits function for handling more data types, but Double isn't an instance of Data.Bits.

Is there an elegant way to memoize `slow?

Answer 1

You could always use ugly-memo. The internals are impure, but it's fast and does what you need (except if the argument is NaN).