This has been my experience. I've learned a bit about FP (mainly by reading books on several FP languages, and attending the SF Bay Area Functional Programmers

This has been my experience. I've learned a bit about FP (mainly by reading books on several FP languages, and attending the SF Bay Area Functional Programmers group back when it was still meeting). However, I have never seen a reasonable way to use a true FP language in my work. Most of what I do is inherently stateful-- at the core are iterative algorithms that update vectors of state variables with small corrections until a problem converges. This is a really hard use case for a pure FP language (i.e., one that "takes away assignment") to shine. That said, learning FP has influenced the way I write the code that pumps numbers into the core update algorithms. Think using PURE and ELEMENTAL functions in Fortran, for example. And of course scientific programming has a rich history of passing functions in to general numerical algorithms. I just don't use closures, or create functions on the fly, or any of that other FP goodness.