SimpleRegex is a VERY simple regex library I created in Haskell. The purpose of the project was so that I could become more proficient in Haskell and functional programming, as well as learn how to parse and execute regular expressions. The program defines a library called SimpleRegex which has two operators: =~ ( a greedy match) and =~? (a non greedy match). This source code is a good example of how to turn a regex string into an NFA using Thompson construction, convert an NFA to DFA using epsilon closures and run a DFA on input strings.
SimpleRegex only supports the | (or), * (closure) and concatenation operators.