implement a procedure for reflowing and displaying paragraphs

gem300.rkt

@@ -42,6 +42,34 @@
             [else
              (values (string->number status) meta)])))))
 
+;; takes one long string and reflows it within an 80 character wide
+;; column
+(define (render-paragraph paragraph)
+  ;; collects from one list of words into another such that the new
+  ;; list does not exceed 80 characters when joined, and returns the
+  ;; new list and remainder of the first list
+  (define (inner-iter acc rst)
+    (let ([line (string-join acc)])
+      (if (or (empty? rst)
+              (> (string-length line) 80))
+          (values acc rst)
+          (inner-iter (append acc (list (car rst)))
+                      (cdr rst)))))
+
+  ;; collects from a list of words into sublists of words such that
+  ;; each sublist is no greater than 80 characters when joined
+  (define (outer-iter acc rst)
+    (if (empty? rst)
+        acc
+        (let-values ([(inner-acc inner-rst)
+                      (inner-iter (list) rst)])
+          (outer-iter (append acc (list inner-acc)) inner-rst))))
+
+  ;; join each sublist into one string, and display one string per
+  ;; line
+  (for-each displayln
+   (map string-join (outer-iter (list) (string-split paragraph)))))
+
 (define commands
   (list
    (cons "default" (lambda (line) (void)))