add a visit link command

its becoming apparent that this doesn't need to be global state, and
can be passed from iteration to iteration in the program loop. this
shall be revisited

gem300.rkt

@@ -7,15 +7,20 @@
 ;; rendered out gemtext document as it shall be shown to the user
 (define document-buffer null)
 
+;; global state which will be the document structure, before rendering
+(define document null)
+
 (define (go-cmd url)
   (if (non-empty-string? url)
       (let-values ([(status meta c-in) (net:get url)])
-        (let-values ([(document) (gmi:parse (port->lines c-in))]
+        (let-values ([(doc) (gmi:parse (port->lines c-in))]
                      [(db-in db-out) (make-pipe #f)])
 
+          (set! document doc)
+
           (set! document-buffer db-in)
           (parameterize ([current-output-port db-out])
-            (gmi:render document))
+            (gmi:render doc))
 
           (let ([remaining (pipe-content-length db-in)])
             (printf "document retrieved. ~a bytes\n" remaining))
@@ -34,20 +39,29 @@
   (iter 10)
   (newline)
   (let ([remaining (pipe-content-length document-buffer)])
-     (printf "~a bytes remaining\n" remaining)))
+    (printf "~a bytes remaining\n" remaining)))
+
+(define (visit-cmd line)
+  (go-cmd (gmi:match-link document (string->number line))))
 
 (define (repl)
   (display "G-300 > ")
 
   (let ([matches (regexp-match #px"(\\w+)\\s*(.*)" (read-line))])
     (cond
-      ;; nothing was given. default command
-      [(not matches)
+      ;; next command. also default
+      [(or (not matches)
+           (string=? (cadr matches) "next")
+           (string=? (cadr matches) "n"))
        (next-cmd)]
 
       ;; go command
-      [(string=? (cadr matches) "go")
-       (go-cmd (caddr matches))]))
+      [(or (string=? (cadr matches) "go")
+           (string=? (cadr matches) "g"))
+       (go-cmd (caddr matches))]
 
+      ;; visit link command
+      [(andmap char-numeric? (string->list (cadr matches)))
+       (visit-cmd (cadr matches))]))
 
   (repl))

gmi.rkt

@@ -1,9 +1,15 @@
 #lang racket
 
-(provide parse render)
+(provide (contract-out
+          [render (-> document? void?)]
+          [parse (-> (listof string?) document?)]
+          [match-link (-> document? integer? (or/c string? #f))]
+          [struct document ((structure (listof (or/c text? link? pre?))))]))
 
 ;; a gemtext document is represented as a list of structs, a struct
 ;; for each type of item in a document.
+(struct document (structure))
+
 (struct text (str))
 (struct link (url str ord))
 (struct pre (str))
@@ -87,7 +93,7 @@
                  'normal
                  link-#)])))
 
-  (iter (list) lines 'normal 1))
+  (document (iter (list) lines 'normal 1)))
 
 ;;;
 ;;; RENDERING
@@ -141,4 +147,19 @@
 
        [(link? line)
         (printf "[~a] ~a\n" (link-ord line) (link-str line))]))
-   document))
+   (document-structure document)))
+
+(define (match-link document id)
+  (define (iter next-structure)
+    (cond
+      [(and (link? (car next-structure))
+            (= (link-ord (car next-structure)) id))
+       (link-url (car next-structure))]
+
+      [(empty? (cdr next-structure))
+       #f]
+
+      [else
+       (iter (cdr next-structure))]))
+
+  (iter (document-structure document)))