Data commit

Task/S-expressions/Scheme/s-expressions.ss

@@ -0,0 +1,44 @@
+(define (sexpr-read port)
+  (define (help port)
+    (let ((char (read-char port)))
+      (cond
+       ((or (eof-object? char) (eq? char #\) )) '())
+       ((eq? char #\( ) (cons (help port) (help port)))
+       ((char-whitespace? char) (help port))
+       ((eq? char #\"") (cons (quote-read port) (help port)))
+       (#t (unread-char char port) (cons (string-read port) (help port))))))
+  ; This is needed because the function conses all parsed sexprs onto something,
+  ; so the top expression is one level too deep.
+  (car (help port)))
+
+(define (quote-read port)
+  (define (help port)
+    (let ((char (read-char port)))
+      (if
+       (or (eof-object? char) (eq? char #\""))
+       '()
+       (cons char (help port)))))
+  (list->string (help port)))
+
+(define (string-read port)
+  (define (help port)
+    (let ((char (read-char port)))
+      (cond
+       ((or (eof-object? char) (char-whitespace? char)) '())
+       ((eq? char #\) ) (unread-char char port) '())
+       (#t (cons char (help port))))))
+  (list->string (help port)))
+
+(define (format-sexpr expr)
+  (define (help expr pad)
+    (if
+     (list? expr)
+     (begin
+      (format #t "~a(~%" (make-string pad #\tab))
+      (for-each (lambda (x) (help x (1+ pad))) expr)
+      (format #t "~a)~%" (make-string pad #\tab)))
+     (format #t "~a~a~%" (make-string pad #\tab) expr)))
+  (help expr 0))
+
+(format-sexpr (sexpr-read
+ (open-input-string "((data \"quoted data\" 123 4.5) (data (!@# (4.5) \"(more\" \"data)\")))")))