Regular expressions and pattern matching

You might wonder why we are talking about regular expressions and pattern matching in this chapter. The reason is simple. In a while, you will learn how to store and read CSV data from plain text files, and you should be able to tell whether the data is valid or not.

Pattern matching is a technique for searching a string for some set of characters, based on a specific search pattern that is based on regular expressions and grammars.

A regular expression is a sequence of characters that defines a search pattern. Every regular expression is compiled into a recognizer by building a generalized transition diagram called a finite automaton. A finite automaton can be either deterministic or nondeterministic. Nondeterministic means that more than one transition out of a state can be possible for the same input. A recognizer is a program that takes a string x as input and can tell whether x is a sentence of a given language or not.

A grammar...