implement rotate right

rover.fnl

@@ -13,15 +13,31 @@
                               :actual actual#
                               })))))
 
-(fn command [rover command]
+(fn rotate [direction rotation]
-  (match rover.direction
+  (let [chooser
-    :n (merge rover {:y (+ rover.y 1)})
+        (match rotation
-    :s (merge rover {:y (- rover.y 1)})
+          :r {
-    :w (merge rover {:x (- rover.x 1)})
+              :n :e
-    :e (merge rover {:x (+ rover.x 1)})))
+              :e :s
+              :s :w
+              :w :n
+              }
+          )]
+    (. chooser direction)))
+
+
+(fn command [rover string]
+  (match string
+    :f (match rover.direction
+         :n (merge rover {:y (+ rover.y 1)})
+         :s (merge rover {:y (- rover.y 1)})
+         :w (merge rover {:x (- rover.x 1)})
+         :e (merge rover {:x (+ rover.x 1)}))
+    :r (merge rover {:direction (rotate rover.direction :r)})
+    _ (assert false (. "unrecognised command " string))))
 
 (fn execute [rover [cmd & cmds]]
-  (let [r1 (command rover)]
+  (let [r1 (command rover cmd)]
     (if (next cmds)
         (r1:execute cmds)
         r1)))
@@ -65,5 +81,13 @@
           (r:execute [:f :f :f])
           {:x 1 :y -2 :direction :s}))
 
+(let [r (rover 2 4 :e)]
+  (expect "Rotates to south when pointing east and asked to turn right"
+          (r:execute [:r]) {:x 2 :y 4 :direction :s}))
+
+(let [r (rover 2 4 :w)]
+  (expect "Rotates to north when pointing west and asked to turn right"
+          (r:execute [:r]) {:x 2 :y 4 :direction :n}))
+
 
 (print "OK")