Simple regex engine written in Haskell.
Instead of using backtracking or finite automata to match strings, it uses derivatives. The idea and algorithm are taken from a blog post by Matt Might.
git clone https://github.com/dwnusbaum/regex-derivatives.git
cd regex-derivatives
cabal update && cabal install
regex '[abc]*d?' '123aaacbccbd'
regex 'Str..' "$(cat ./Main.hs)"
The output is colored like the output of ag.