add S W E

src/main.rs

@@ -9,7 +9,13 @@ mod rover {
     type Rover = (i32, i32, Facing);
 
     pub fn forward((lon, lat, direction) : Rover) -> Rover {
-	(lon as i32, lat - 1 as i32, direction)
+	let (xoff, yoff) = match direction {
+	    Facing::N  => ( 0, -1),
+	    Facing::E  => ( 1,  0),
+	    Facing::S  => ( 0,  1),
+	    Facing::W  => (-1,  0)
+	};
+	(lon + xoff as i32, lat + yoff as i32, direction)
     }
 }
 
@@ -27,4 +33,25 @@ mod tests {
 	assert_eq!(rover::forward(r),
 		   (1 as i32, 2 as i32, rover::Facing::N));
     }
+
+    #[test]
+    fn move_south() {
+	let r = (1 as i32, 1 as i32, rover::Facing::S);
+	assert_eq!(rover::forward(r),
+		   (1 as i32, 2 as i32, rover::Facing::S));
+    }
+
+    #[test]
+    fn move_west() {
+	let r = (1 as i32, 1 as i32, rover::Facing::W);
+	assert_eq!(rover::forward(r),
+		   (0 as i32, 1 as i32, rover::Facing::W));
+    }
+
+    #[test]
+    fn move_east() {
+	let r = (1 as i32, 1 as i32, rover::Facing::E);
+	assert_eq!(rover::forward(r),
+		   (2 as i32, 1 as i32, rover::Facing::E));
+    }
 }