> Clearly there was plenty of room for speeding up our string matching. We considered binding the Rust library, but due to the way that Haskell’s foreign function interface interacts with the garbage collector, passing a string to a foreign function requires copying it. That copy alone puts any foreign library at a significant disadvantage, so we decided to see how close we could get in Haskell alone.

It's a shame Haskell copies strings across FFI boundaries, because binding the Rust version would have been almost as fast, with (presumably) significantly less effort.