move obstacle checking down from command to drive

rover.fnl

@@ -6,18 +6,28 @@
       (< 180 x)   (wrap-longitude (- x 360))
       x))
 
+(fn at-obstacle? [{: x : y : obstacles}]
+  (any obstacles
+       (fn [[ox oy]] (and (= ox x) (= oy y)))))
+
+(fn try-to-drive [{: x : y : direction : stopped &as r} distance]
+  (let [distance
+        (if (. {:w true :e true} direction)
+            (/  distance (math.cos (/ (* math.pi y) 180)))
+            distance)]
+    (match direction
+      :n {:y (+ y distance)}
+      :s {:y (- y distance)}
+      :w {:x (wrap-longitude (- x distance))}
+      :e {:x (wrap-longitude (+ x distance))})))
+
 (fn drive [{: x : y : direction : stopped &as r} distance]
   (if stopped
       r
-      (let [distance
-            (if (. {:w true :e true} direction)
-                (/  distance (math.cos (/ (* math.pi y) 180)))
-                distance)]
-        (match direction
-          :n {:y (+ y distance)}
-          :s {:y (- y distance)}
-          :w {:x (wrap-longitude (- x distance))}
-          :e {:x (wrap-longitude (+ x distance))}))))
+      (let [next-move (merge r (try-to-drive r distance))]
+        (if (at-obstacle? next-move)
+            (merge r {:stopped [next-move.x next-move.y]})
+            next-move))))
 
 (fn turn-left [{: x : y : direction}]
   (if (= y 90)
@@ -43,22 +53,14 @@
             }
            (. direction))}))
 
-(fn at-obstacle? [{: x : y : obstacles}]
-  (any obstacles
-       (fn [[ox oy]] (and (= ox x) (= oy y)))))
-
 (fn command [rover string]
-  (let [next-move
-        (merge rover
-               (match string
-                 :f (drive rover 1)
-                 :b (drive rover -1)
-                 :r (turn-right rover)
-                 :l (turn-left rover)
-                 _ (assert false (. "unrecognised command " string))))]
-    (if (at-obstacle? next-move)
-        (merge rover {:stopped [next-move.x next-move.y]})
-        next-move)))
+  (merge rover
+         (match string
+           :f (drive rover 1)
+           :b (drive rover -1)
+           :r (turn-right rover)
+           :l (turn-left rover)
+           _ (assert false (. "unrecognised command " string)))))
 
 (fn fudge-for-pole [{: y &as r}]
   (if (= y 90)