The main problem is probably creating and traversing the strings, although I have not benchmarked it. This version
https://gist.github.com/Codas/894694eea247aaacf35f
runs about 4 times faster than the python version on my machine.
It does use some libraries that are not in the haskell platform though.
The rust compiler itself would certainly not be the best resource, but I thing servo[1] would do just fine.
Also, you can just look at some rust repositories[2] on github.
In addition to those jbeja mentioned, there is also fiplr[1], somewhat in the spirit of ctrl-p, command-t etc. for vim.
One favorite tweak of mine for file finders like this in general: rewrite the dir listing to use "git ls-files -co --exclude-standard". This obviously only works in git projects (similar commands exist for mercurial I think), but is really fast and most of the time is exactly what I want.
You might also want to take a look at the ergodox: http://ergodox.org/
It's not so easy to buy as its just a DIY project. Massdrop organizes some group buys [1], next one should be due anytime this year.
It does use some libraries that are not in the haskell platform though.