start firmly defining module boundaries for gmi parser

gmi.rkt

@@ -1,9 +1,14 @@
 #lang racket
 
-(provide parse render)
+(provide (contract-out
+          [render (-> document? void?)]
+          [parse (-> (listof string?) document?)]
+          [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 +92,7 @@
                  'normal
                  link-#)])))
 
-  (iter (list) lines 'normal 1))
+  (document (iter (list) lines 'normal 1)))
 
 ;;;
 ;;; RENDERING
@@ -141,4 +146,4 @@
 
        [(link? line)
         (printf "[~a] ~a\n" (link-ord line) (link-str line))]))
-   document))
+   (document-structure document)))