A-level Computing/AQA/Paper 1/Theory of computation/Regular languages

Finite state machines Regular Languages Finite State Machines with and without Output (Mealy Machines) Maths for Regular Expressions Regular Expressions Regular Languages Backus-Naur Form for Context-Free Languages Regular Expressions A regular expression is an expressions used to specify a set of strings that satisfy given conditions (A sequence of characters that define a search pattern). They are used by programmers and computers to work with text patterns. The most popular implementations are in search engines and search & replace dialogues in word processors. Most programming languages support regular expressions, but the most common symbols are described below: | A vertical bar separates alternatives e.g. (D|d)is(c|k) ? A question mark indicates zero or one of the preceding element e.g. colou?r * An asterisk indicates zero or more of the preceding element e.g. aa and aabbb would match aab* + A plus indicates one or more of the preceding element e.g. abc and abccc would match abc+ If your programming language supports regular expressions, such as Python, the syntax might be different.