sand.flan asks for length

Two sites, and the second is the subtle one: the let binds a local named
length from (length coll), which reads because a sequential let checks an
initialiser before the name it binds exists. That was the reason for the
rename -- len is a variable now.

sand.flan

@@ -28,7 +28,7 @@
 (defn insertion-sort [coll [$t]] ()
   {:where (ordered? $t)}
   (let [i 1
-        length (len coll)]
+        length (length coll)]
     (while (and (< i length))
       (let [j i]
         (while (and (> j 0)
@@ -52,7 +52,7 @@
   (set velocity (zeroed)))
 
 (defn next-color [] ()
-  (set current-color (% (+ current-color 1) (len colors))))
+  (set current-color (% (+ current-color 1) (length colors))))
 
 (defn paint-at [row i32  col i32] ()
   (let [half (/ brush-size 2)]