beautiful-racket/beautiful-racket-demo/basic-demo/lexer.rkt

#lang br
(require brag/support)

(define-lex-abbrev digits (:+ (char-set "0123456789")))

(define basic-lexer
  (lexer-srcloc
   ["\n" (token 'NEWLINE lexeme)]
   [whitespace (token lexeme #:skip? #t)]
   [(from/stop-before "rem" "\n") (token 'REM lexeme)]
   [(:or "print" "goto" "end"
         "+" ":" ";") (token lexeme lexeme)]
   [digits (token 'INTEGER (string->number lexeme))]
   [(:or (:seq (:? digits) "." digits)
         (:seq digits "."))
    (token 'DECIMAL (string->number lexeme))]
   [(:or (from/to "\"" "\"") (from/to "'" "'"))
    (token 'STRING
           (substring lexeme
                      1 (sub1 (string-length lexeme))))]))

(provide basic-lexer)