defines a procedure used for looking up links by id in a document

gmi.rkt

@@ -3,6 +3,7 @@
 (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
@@ -147,3 +148,18 @@
        [(link? line)
         (printf "[~a] ~a\n" (link-ord line) (link-str line))]))
    (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)))