A straightforward library for complex numbers.
$ futhark pkg add github.com/diku-dk/complex
$ futhark pkg sync
$ futhark repl
> import "lib/github.com/diku-dk/complex/complex"
> module c64 = mk_complex f64
> let c = c64.mk 1 2
> c64.conj c
(1.0f64, -2.0f64)