we can drive a rover with sequence of commands as string

src/main.rs

@@ -8,7 +8,7 @@ mod rover {
     #[derive(Debug, PartialEq, Copy, Clone)]
     pub enum Rotation { Left, Right }
 
-    type Rover = (i32, i32, Facing);
+    pub type Rover = (i32, i32, Facing);
 
     fn velocity(direction : &Facing) -> (i32, i32) {
 	match direction {
@@ -55,6 +55,29 @@ mod rover {
 }
 
 
+mod driver {
+    use super::rover;
+
+    fn perform_insn(command: &str, rover: &rover::Rover) -> rover::Rover {
+	match command {
+	    "f" => rover::forward(&rover),
+	    "b" => rover::backward(&rover),
+	    "l" => rover::rotate(&rover, rover::Rotation::Left),
+	    "r" => rover::rotate(&rover, rover::Rotation::Right),
+	    _ => rover.clone()
+	}
+    }
+
+    pub fn execute(rover: &rover::Rover, instructions: &str) -> rover::Rover {
+	if instructions.is_empty() {
+	    rover.clone()
+	} else {
+	    let (first, rest) = instructions.split_at(1);
+	    execute(&perform_insn(first, rover), rest)
+	}
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -112,4 +135,12 @@ mod tests {
 	    (_, _, facing) => assert_eq!(facing, rover::Facing::W)
 	}
     }
+
+    #[test]
+    fn drive() {
+	let r = (1 as i32, 1 as i32, rover::Facing::S);
+	assert_eq!(driver::execute(&r, "ffrf"),
+		   (0 as i32, 3 as i32, rover::Facing::W));
+    }
+
 }