oops, forgot to implement backwards

rover.fnl

@@ -39,6 +39,11 @@
                 :s {:y (- rover.y 1)}
                 :w {:x (- rover.x 1)}
                 :e {:x (+ rover.x 1)})
+           :b (match rover.direction
+                :n {:y (- rover.y 1)}
+                :s {:y (+ rover.y 1)}
+                :w {:x (+ rover.x 1)}
+                :e {:x (- rover.x 1)})
            :r {:direction (turn-right rover.direction)}
            :l {:direction (turn-left rover.direction)}
            _ (assert false (. "unrecognised command " string)))))
@@ -86,6 +91,14 @@
           (execute r [:f :f :f])
           {:x 1 :y -2 :direction :s}))
 
+(let [r (rover 3 2 :s)]
+  (expect "Moves north when pointing south and asked to move backward"
+          (execute r [:b]) {:x 3 :y 3 :direction :s}))
+
+(let [r (rover 3 2 :e)]
+  (expect "Moves west when pointing east and asked to move backward"
+          (execute r [:b]) {:x 2 :y 2 :direction :e}))
+
 (let [r (rover 2 4 :e)]
   (expect "Rotates to south when pointing east and asked to turn right"
           (execute r [:r]) {:x 2 :y 4 :direction :s}))