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A very simple example showing how to use Racket's lexing and parsing utilities
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#lang racket | |
(require parser-tools/lex | |
(prefix-in re- parser-tools/lex-sre) | |
parser-tools/yacc) | |
(provide (all-defined-out)) | |
(define-tokens a (NUM)) | |
(define-empty-tokens b (+ - EOF)) | |
(define-lex-trans number | |
(syntax-rules () | |
((_ digit) | |
(re-: (re-? (re-or "-" "+")) (uinteger digit) | |
(re-? (re-: "." (re-? (uinteger digit)))))))) | |
(define-lex-trans uinteger | |
(syntax-rules () | |
((_ digit) (re-+ digit)))) | |
(define-lex-abbrevs | |
(digit10 (char-range "0" "9")) | |
(number10 (number digit10))) | |
(define simple-math-lexer | |
(lexer | |
((re-+ number10) (token-NUM (string->number lexeme))) | |
("-" (token--)) | |
("+" (token-+)) | |
;; recursively calls the lexer which effectively skips whitespace | |
(whitespace (simple-math-lexer input-port)) | |
((eof) (token-EOF)))) | |
(define simple-math-parser | |
(parser | |
(start exp) | |
(end EOF) | |
(error void) | |
(tokens a b) | |
(precs (left - +)) | |
(grammar | |
(exp ((NUM) $1) | |
((exp + exp) (+ $1 $3)) | |
((exp - exp) (- $1 $3)))))) | |
(define (lex-this lexer input) (lambda () (lexer input))) | |
(let ((input (open-input-string "3 - 3.3 + 6"))) | |
(simple-math-parser (lex-this simple-math-lexer input))) |
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