Alex is a tool for generating lexical analysers in Haskell, given a
description of the tokens to be recognised in the form of regular
expressions. It is similar to the tools lex and flex for C/C++.

Alex takes a description of tokens based on regular expressions and
generates a Haskell module containing code for scanning text
efficiently. Alex is designed to be familiar to exisiting lex users,
although it does depart from lex in a number of ways.