FLEX (Fast Lexical Analyzer Generator) is a tool used for generating lexical analyzers (also known as scanners or lexers), developed by Vern Paxson in C around 1987. It is commonly used in conjunction with Berkeley Yacc or GNU Bison parser generators. Both Flex and Bison offer greater flexibility and produce faster code compared to their predecessors, Lex and Yacc.
Bison generates a parser from a user-provided input file, while Flex generates the yylex() function, which is automatically created when provided with a .l file. This yylex() function is then invoked by the parser to retrieve tokens from the current token stream.
