ReGex

Regular Expressions is a an example of a Regular Language

This is a language to specify and discover patterns in strings.
Cheatsheet.

In Java

• Find strings
• Uses a pattern to compile a string pattern into a recognizer (a program that scans input and checks for desired pattern)
• Uses a matcher to apply Pattern to a string

In a compilers sense…

• We use regex to segment identifiers and numbers separated by whitespace

Regex Combines Characters with

• Concatenation $xy$: One thing after another
• Repetition $x\ast$: *, something repeated
• Alternation $x|y$: One thing or another (OR)
• Parentheses ($()$): Used like in math
• Empty String ($\lambda$): Nothing
• Constant ($x$): One thing