diff --git a/.guix/modules/bloatrunner.scm b/.guix/modules/bloatrunner.scm
index 1a1903f..76a4c8e 100644
--- a/.guix/modules/bloatrunner.scm
+++ b/.guix/modules/bloatrunner.scm
@@ -69,7 +69,7 @@
                                     (wrap-program (string-append out "/bin/bloatrunner")
                                                   `("GUILE_LOAD_PATH" ":" prefix (,mods))
                                                   `("GUILE_LOAD_COMPILED_PATH" ":" prefix (,objs))
-                                                  `("ASSET_DIR" ":" prefix (,(string-append out "/share/bloatrunner")))
+                                                  `("ASSET_DIR" ":" prefix (,(string-append out "/share/bloatrunner/assets")))
                                                   )))))
       ))
    (native-inputs
diff --git a/game/main.scm b/game/main.scm
index a8cbd48..a59a713 100644
--- a/game/main.scm
+++ b/game/main.scm
@@ -35,13 +35,15 @@
 (define state 'running)
 
 (define (load)
+  "Load the game initial game state."
   (assets-load)
   (render-level-load)
-  (set! levels (assets-map-levels level-parse-file))
+  (set! levels (assets-map-levels level-parse))
   (load-level)
   (set! repl (spawn-coop-repl-server)))
 
 (define (load-level)
+  "Load the next level and reset game state."
   (set! level (car levels))
   (set! levels (cdr levels))
   (render-level-set! level)
@@ -51,6 +53,7 @@
   (set! foods (food-load level)))
 
 (define (update dt)
+  "Update the game state."
   (poll-coop-repl-server repl)
   (set! hero (hero-update hero level inputs keys (food-total-calories-eaten foods) dt))
   (set! others (map (lambda (other) (other-update other level hero others dt)) others))
@@ -60,11 +63,11 @@
       (set! state 'lost))
   (if (level-same-cell? (hero-position hero) (level-find-goal level))
       (if (null? levels)
-          (set! status 'won) 
-          (load-level)))
-  )
+          (set! state 'won) 
+          (load-level))))
 
 (define (render-level)
+  "Render the level and entities for the running state"
   (render-level-draw level)
   (for-each render-other others)
   (render-keys keys (level-find-goal level))
@@ -72,17 +75,26 @@
   (render-hero hero))
 
 (define (draw _alpha)
+  "Draw the game screen depending on state"
   (case state 
     ((won)  (render-victory))
     ((lost) (render-defeat))
     (else (render-level))))
 
+
+;; Input handling
+;;  keep a set of buttons which are currently pressed
+;; 
+
 (define (set-add set item)
-(if (member item set)
-    set
-    (cons item set)))
+  "Add an item to a list if it is not already present."
+  (if (member item set)
+      set
+      (cons item set)))
+
 
 (define (key-press key _modifiers _repeat?)
+  "Handle key press events by adding the input to the inputs set."
   (set! inputs
     (cond ((eq? key 'left) (set-add inputs 'left))
           ((eq? key 'right) (set-add inputs 'right))
@@ -94,6 +106,7 @@
 
 
 (define (key-release key _modifiers)
+  "Handle key release events by removing the input from the inputs set."
   (set! inputs
     (cond ((eq? key 'left) (delete 'left inputs))
           ((eq? key 'right) (delete 'right inputs))
@@ -103,6 +116,7 @@
           (else inputs))))
 
 (define (launch-game args)
+  "Launch the game with the given arguments."
   (run-game 
    #:window-title "Bloatrunner"
    #:load (lambda () (load))
diff --git a/game/model/hero.scm b/game/model/hero.scm
index a51b77f..29db12e 100644
--- a/game/model/hero.scm
+++ b/game/model/hero.scm
@@ -91,9 +91,11 @@
 
 (define (hero-update hero level inputs keys calories-eaten dt)
   (let* ((new-runner (runner-update (hero-runner hero) level inputs dt))
-         (new-runner (if (blocked-by-door? level keys 
-                                           (runner-position new-runner)
-                                           (hero-bloat hero))
+         (new-runner (if (blocked-by-door? 
+                          level 
+                          keys 
+                          (runner-position new-runner)
+                          (hero-bloat hero))
                          (hero-runner hero)
                          new-runner
                          ))
@@ -123,10 +125,13 @@
 (let* ((level (level-parse "WWGWW\nW.H.W\nW.P.W\nWWWWW\n"))
        (hero (hero-load level))
        (goal-position (level-find-goal level)))
-  (test-assert (blocked-by-door? level '(dummy-key) goal-position))
-  (test-assert (not (blocked-by-door? level '() goal-position)))
-  (test-assert (blocked-by-door? level '(dummy-key) (vec2- goal-position (vec2 0 -15))))
-  (test-assert (not (blocked-by-door? level '(dummy-key) (vec2- goal-position (vec2 0 -16))))))
+  (test-assert (blocked-by-door? level '(dummy-key) goal-position 1.0))
+  (test-assert (not (blocked-by-door? level '() goal-position 1.0)))
+  (test-assert (blocked-by-door? level '(dummy-key) (vec2- goal-position (vec2 0 -15)) 1.0))
+  (test-assert (not (blocked-by-door? level '(dummy-key) (vec2- goal-position (vec2 0 -16)) 1.0)))
+  (test-assert (blocked-by-door? level '() goal-position 1.55))
+  
+  )
 
 (test-end "hero-model")
 
diff --git a/game/model/level.scm b/game/model/level.scm
index 3b72937..a12ed55 100644
--- a/game/model/level.scm
+++ b/game/model/level.scm
@@ -39,6 +39,7 @@
   (entities level-entities))
 
 (define (parse-tile c)
+  "Parse a character into a tile type"
   (case c
     ((#\W) 'wall)
     ((#\B) 'brick)
@@ -52,6 +53,7 @@
     (else 'empty)))
 
 (define (content->lines content)
+  "Parse a string into a list of lines, ignoring empty lines and comments"
   (filter (lambda (line) (not (string-null? line)))
           (map
            (lambda (line) 
@@ -62,6 +64,7 @@
 
 
 (define (parse-lines lines)
+  "Parse a list of lines into a list of tiles"
   (fold append
         '()
         (map
@@ -70,6 +73,7 @@
          lines)))
 
 (define (level-parse content)
+  "Parse a level from a string"
   (let* ((lines (content->lines content))
          (width (string-length (car lines)))
          (height (length lines))
@@ -77,20 +81,19 @@
                  (parse-lines lines))))
     (%make-level width height tiles)))
 
-(define (level-parse-file filename)
-  (level-parse (call-with-input-file filename get-string-all)))
-
-
 (define (level-tile-at-row-col level row col )
+  "Get the tile at a given row and column"
   (let ((index (+ (* row (level-width level)) col)))
     (vector-ref (level-tiles level) index)))
 
 (define level-cell-size 16)
 
 (define (coord->cell coord)
+  "Convert a screen coordinate to a vector cell index"
   (inexact->exact (floor (/ coord level-cell-size))))
 
 (define (level-tile-at level position )
+  "Get the tile at a given screen position"
   (let ((x (vec2-x position))
         (y (vec2-y position)))
     (level-tile-at-row-col level (coord->cell y) (coord->cell x))))
@@ -168,8 +171,8 @@
 (test-equal (parse-tile #\F) 'bad-food)
 (test-equal (parse-tile #\f) 'good-food)
 
-(test-equal (level-width (level-parse-file "assets/levels/level-001.map")) 40)
-(test-equal (level-height (level-parse-file "assets/levels/level-001.map")) 30)
+(test-equal (level-width (level-parse (read-level-map "level-001.map"))) 40)
+(test-equal (level-height (level-parse (read-level-map "level-001.map"))) 30)
 
 (test-equal 
     (level-tile-at-row-col (level-parse "WWWWW\nWP GW\nWWWWW\n") 1 1)
diff --git a/game/util/assets.scm b/game/util/assets.scm
index a2647ba..adf64ce 100644
--- a/game/util/assets.scm
+++ b/game/util/assets.scm
@@ -3,7 +3,7 @@
   #:use-module (ice-9 textual-ports)
   #:use-module (chickadee graphics texture)
   #:use-module (chickadee graphics color)
-  #:export (assets-load assets-file-name tile-texture tile-atlas hero-texture hero-atlas assets-map-levels)
+  #:export (assets-load assets-load-image tile-texture tile-atlas hero-texture hero-atlas assets-map-levels read-level-map)
   
   )
 
@@ -14,11 +14,11 @@
 (define hero-atlas #f)
 
 (define (assets-location)
+  "find the location of the assets directory. The location is specified
+   by the ASSET_DIR environment variable, or defaults to 'assets' in the
+   current directory."
   (pk "Assets location: "
-      (if (current-filename)
-          (string-append (dirname (current-filename)) "/../../assets")
-          (or (getenv "ASSET_DIR") "." )))
-  )
+      (or (getenv "ASSET_DIR") "assets" )))
 
 (define (assets-file-name . names)
   "Return the full path of a file in the assets directory. The file is
@@ -29,18 +29,31 @@
 
 
 (define (read-level-map filename)
-  (call-with-input-file filename get-string-all))
+  "Read a level map from a file. The map is a list of strings, where each
+   string is a row of the map. The map is read from the file in the
+   'levels' directory."
+  (call-with-input-file (assets-file-name "levels" filename) get-string-all))
+
+(define (level-map? filename )
+  "Return true if the filename is a level map file. Level map files have
+   the extension '.map'."
+  (string-suffix? ".map" filename))
 
 (define (assets-map-levels f)
-  (map f 
-       (map (lambda (filename)(assets-file-name "levels" filename))
-            (scandir (assets-file-name "levels") 
-                     (lambda (filename) (string-suffix? ".map" filename ))))))
+  "Apply a function to each level map file in the 'levels' directory. The
+   function is passed the filename of the level map file."
+  (map 
+   (compose f read-level-map)  
+   (scandir (assets-file-name "levels") level-map?)))
 
 (define (assets-load-image filename)
+  "Load an image from a file in the assets directory. The filename is
+   specified as a list of names, which are joined together. The image is
+   returned as a texture."
   (load-image (assets-file-name "images" filename)))
 
 (define (assets-load)
+  "Load all the assets for the game."
   (set! tile-texture (assets-load-image "simples_pimples.png"))
   (set! tile-atlas (split-texture tile-texture 16 16))
   
diff --git a/pre-inst-env.in b/pre-inst-env.in
index 881f142..0afa99f 100644
--- a/pre-inst-env.in
+++ b/pre-inst-env.in
@@ -5,6 +5,6 @@ abs_top_builddir="`cd "@abs_top_builddir@" > /dev/null; pwd`"
 
 export GUILE_LOAD_COMPILED_PATH="$abs_top_builddir${GUILE_LOAD_COMPILED_PATH:+:}$GUILE_LOAD_COMPILED_PATH"
 export GUILE_LOAD_PATH="$abs_top_builddir:$abs_top_srcdir${GUILE_LOAD_PATH:+:}:$GUILE_LOAD_PATH"
-export PATH="$abs_top_builddir/scripts:$PATH"
+export PATH="$abs_top_builddir:$PATH"
 
 exec "$@"