Regular Expressions and Automata using Haskell

The paper begins with definitions of regular expressions, and how strings are matched to them; this also gives our first Haskell treatment also. After describing the abstract data type of sets we define non-deterministic finite automata, and their implementation in Haskell. We then show how to build an NFA corresponding to each regular expression, and how such a machine can be optimised, first by transforming it into a deterministic machine, and then by minimising the state space of the DFA. We conclude with a discussion of regular definitions, and show how recognisers for strings matching regular definitions can be built.