make turn-left/right return mergable tables

this gives greater symmetry with `drive`

rover.fnl

@@ -21,30 +21,32 @@
     :e {:x (+ x distance)}))
 
 (fn turn-left [direction]
-  (-> {
-       :n :w
-       :w :s
-       :s :e
-       :e :n
-       }
-      (. direction)))
+  {:direction
+   (-> {
+        :n :w
+        :w :s
+        :s :e
+        :e :n
+        }
+       (. direction))})
 
 (fn turn-right [direction]
-  (-> {
-       :n :e
-       :e :s
-       :s :w
-       :w :n
-       }
-      (. direction)))
+  {:direction
+   (-> {
+        :n :e
+        :e :s
+        :s :w
+        :w :n
+        }
+       (. direction))})
 
 (fn command [rover string]
   (merge rover
          (match string
            :f (drive rover 1)
            :b (drive rover -1)
-           :r {:direction (turn-right rover.direction)}
-           :l {:direction (turn-left rover.direction)}
+           :r (turn-right rover.direction)
+           :l (turn-left rover.direction)
            _ (assert false (. "unrecognised command " string)))))
 
 (fn execute [rover cmds]