7. Javascript

Remember when you ran this code?

r = UsedRobot()
inspect(r)

We are going to do the equivalent with Javascript.

At the very top of the Reeborg’s World window, click to open the “Additional options” dialog and select Javascript instead of Python. Then run the following code:

var r = new UsedRobot();
inspect(r);

Here is what I see when I do this:

body
at_goal()
build_wall()
front_is_clear()
carries_object()
is_facing_north()
move()
put()
token_here()
right_is_clear()
object_here()
take()
turn_left()

So, nothing that starts and end with a double underscore, and we see body as we had in the Python code, but will also see some familiar methods like at_goal(), move() and many others.

Now we are ready to look at some code.

Do this!

Execute the following Javascript code and look at the result in the Diary.

var r = new UsedRobot();
view_source(r.turn_left);

Make sure the code is exactly as written above. Note that I use view_source instead of inspect which, as it turns out, would not help me at all in this case.

Based on the result that I see printed in Reeborg’s Diary

function () {
        RUR.control.turn_left(this.body);
    }

my next guess is to execute the following.

var r = new UsedRobot();
view_source(RUR.control.turn_left);

After doing so, I see the following:

function (robot){
    "use strict";
    robot._prev_orientation = robot._orientation;
    robot._prev_x = robot.x;
    robot._prev_y = robot.y;
    robot._orientation += 1;  // could have used "++" instead of "+= 1"
    robot._orientation %= 4;
    RUR.control.sound_id = "#turn-sound";
    RUR.rec.record_frame();
}

As mentioned above, you might see something slightly different. Here is the equivalent Python code:

def unknown_function_name (robot):
    robot._prev_orientation = robot._orientation
    robot._prev_x = robot.x
    robot._prev_y = robot.y
    robot._orientation += 1
    robot._orientation %= 4
    RUR.control.sound_id = "#turn-sound"
    RUR.rec.record_frame()

We will come back to this code sample later; for now, remember that we were talking about “recording frames” ... It looks as though the last instruction is the one we were looking for. Time to go back to coding in Python. Select Python as the programming language at the top of Reeborg’s World window before running the following program.

Try this!

Select world Empty and run the following code with the code highlighting turned off to confirm that you can add new capabilities to Reeborg and show its effect properly at each step.

class Teleporter(UsedRobot):

    def jump(self, x, y):
        self.body.x = x
        self.body.y = y
        RUR.rec.record_frame()

jumper = Teleporter()
jumper.jump(3, 5)
jumper.jump(7, 2)

Try again afterwards with the code highlighting turned on. Can you figure out what is going on?

Your turn!

Design a robot class that can “hop” horizontally, only increasing the x coordinate by 1 each time (like in a move method) but effectively jumping over walls. Create a robot instance and have it solve the hurdles challenges, Hurdles 1 to Hurdles 4, by going in a straight line, straight through walls! For each existing world, you will first have to click on “Additional options” followed by “Edit world” and remove the robot already present; save the corresponding world in a name of your choice; that way, it will be added to the world menu.

A complete solution can be written in only 7 lines of code.

Hint

You can move the robot in the desired way by incrementing its x variable as follows:

self.body.x += 1