diff --git a/design.org b/design.org
index 39260d7..0a10a4b 100644
--- a/design.org
+++ b/design.org
@@ -55,3 +55,16 @@ A node is a data structure containing the following elements:
 + Type (typeval)
 + Text component (optional textval)
 + Preformat (boolean)
+* Preformat calculation
+The currently visited node should be marked "preformat" when:
+| *current preformat mode* | *visited node type* | *preformat?* |
+|--------------------------+---------------------+--------------|
+| t                        | preformat           | nil          |
+| nil                      | preformat           | t            |
+| t                        | any other           | t            |
+| nil                      | any other           | nil          |
+
+a := current preformat mode is t
+b := newly visited node is a PREFORMAT node
+
+(not a and b) or (a and not b)
diff --git a/src/white-tiger.lisp b/src/white-tiger.lisp
index 6637218..1cfb64f 100644
--- a/src/white-tiger.lisp
+++ b/src/white-tiger.lisp
@@ -36,15 +36,25 @@
 (defun type-of-file (filename)
   (map 'list #'type-of-line (read-file filename)))
 
-(defun line-to-node (line preformat)
-  ;; TODO: Handle preformat mode termination lines
+(defun xor (a b)
+  (or (and (not a) b) (and a (not b))))
+
+(defun line-to-node (line type preformat)
   (make-node
    :preformat preformat
-   
-   ))
+   ;; TODO: Split line on first whitespace; use cdr for text component
+   :type type
+   :text-component ""))
 
-(defun parse-gemtext-file ()
-  t)
+(defun parse-gemtext-file (line-list preformat-mode)
+  (if (= (length line-list) 0)
+      nil
+      ;; Parse the line. If this line is a PREFORMAT, toggle the boolean moving forward.
+      (let ((line-type (type-of-line (car line-list))))
+	(cons (line-to-node (car line-list) line-type (if (eq line-type :preformat) nil preformat-mode))
+	      (parse-gemtext-file (cdr line-list) (if (eq line-type :preformat) (not preformat-mode) preformat-mode))))))
 
-(defun start () t)
+(defun start (filename)
+  (let ((file-contents (read-file filename)))
+    (parse-gemtext-file file-contents nil)))