I was interested to see a Runge-Kutta package posted to this list recently, particularly as I have a fairly simple-minded non-adaptive RK "generator": an AWK script that takes a table and some optional stuff and spits out C. The Haskell package is, of course, a lot prettier than my AWK program, as well as offering some adaptive methods, which is important. We can imagine a spectrum of RK packages: (1) Higher order function taking some runtime parameters. That's what we got. (2) The same specialised for a known table at compile time. Doable using the code that we were given plus SPECIALIZE pragmas. I don't how well that works across modules. (3) A generator that writes Haskell source. (4) Template Haskell. (5) A generator that generates native code to be called through FFI. The question is, how do you decide what's the appropriate approach?