Lexical Analysis

exl.scm

(define scanner-exl '( (white-sp (whitespace) skip) (comment ("#" (arbno (not #\newline))) skip) (identifier (letter (arbno (or letter digit))) make-symbol) (number (digit (arbno digit)) make-number) ) )

This is the definition of the lexical structure of the Example Language.

It consists of a list of token definitions where each token definition is a list with a token name, a regular expression, and an action:

Token Name Regular Expression Action

white-sp \s+ skip

comment #.*\n skip

identifier [A-Za-z][A-Za-z0-9]* make-symbol

number \d+ make-number

Regular expressions can also be formed by some list structure. arbno means ``arbitrary number'' and represents the Kleene star.

All delimiters and keywords that are used in form of string constants in the grammar do not need to be included here.