For the past 8 or so years davean has been relying on Haskell to keep his code performant and functional.
Talks I've Given
Smallpt-hs: Porting a Raytracer's Performance to Haskell
Featuring davean scies and Siddharth Bhat
Let's tune a Haskell program to be as fast as C! (1) Begin with smallpt, a 100 line C raytracer that we naively port to Haskell. (2) balk at the 5x performance slowdown. (3) Roll up our sleeves. (4) Performance parity!haskell raytracer porting