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Parser for simplest S-expression by using 1-character input in Scheme
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(define *lh* #f) | |
(define (get-token) | |
(define (put-c1 x) (set! *lh* x)) | |
(define (null-c1) (set! *lh* #f)) | |
(define (get-c1) (if *lh* (let ((lh *lh*)) (null-c1) lh) (read-char))) | |
(define (tstring t) (list->string (reverse t))) | |
(define (skip-spaces) | |
(do ((c (get-c1) (get-c1))) | |
((not (member c (string->list " \n\r"))) (put-c1 c)))) | |
(let loop ((c (get-c1)) (t '())) | |
(cond ((member c (string->list " \n\r")) | |
(cond ((null? t) | |
(skip-spaces) | |
(loop (get-c1) t)) | |
(else (tstring t)))) | |
((eq? c #\() (skip-spaces) (string c)) | |
((eq? c #\)) | |
(if (null? t) (string c) (begin (put-c1 c) (tstring t)))) | |
(else (loop (get-c1) (cons c t)))))) | |
(define (sread) | |
(define (slist) | |
(let ((t (get-token))) | |
(cond ((equal? t ")") '()) | |
((equal? t "(") (let ((h (slist))) (cons h (slist)))) | |
(else (cons t (slist)))))) | |
(let ((t (get-token))) | |
(if (equal? t "(") (slist) t))) | |
(write (sread)) (newline) | |
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