Hurdles yet again!
==================

Reeborg lives in Canada where it not only can rain or be sunny, but snow
can also be falling ... usually not all three at the same time ... but
it does happen... Let's suppose that only one of those can happen. Then,
Reeborg could be faced with the following choices::

    if ( it_rains() ) {
        play_indoors();
    } else if ( it_snows() ){
        go_skiing();
    } else {
        go_swimming(); // assuming it is warm!
    }

Notice the use of ``else`` for choices 2 and 3, and the additional
``if`` statement for the second case. If we took into account other
possible weather phenomena, like hail, thunder, fog, drizzle, etc., we
could add other choices using additional ``else if {...}`` code blocks.

How to think of ``if/else if/ ... /else`` statements
----------------------------------------------------

A series of ``if/else if/ ... /else`` statements is equivalent to
inserting the **first** code block that evaluates to ``true``. Thus::

    if ( false ) {
        do_1();
    } else if ( true ){
        do_2();
    } else if ( true ){
        do_3();
    } else {
        do_4();
    }

is equivalent to::

    do_2();

whereas::

    if ( false ) {
        do_1();
    } else if ( false ){
        do_2();
    } else if ( false ){
        do_3();
    } else {
        do_4();
    }

is equivalent to::

    do_4();

etc.

Back to hurdles
---------------

Just two lessons ago, you wrote a program that worked for worlds
**Hurdles 1** and **Hurdles 2** but not for **Hurdles 3**. Your program was likely
something like this::

    function jump_over_hurdle() {
        // some suitable definition
    }

    function move_and_jump_until_done () {
        move();
        if ( at_goal() ) {
            done();
        }
        jump_over_hurdle();
    }

    repeat(move_and_jump_until_done, 42);

The reason it is not working for **Hurdles 3** is that it is written with
the assumption that the hurdles are evenly spaced. Let's use our new
condition ``front_is_clear()`` and keyword ``else`` to change that.

Here's a new program that should work for the world we mentioned above,
provided you fill in the missing pieces.::

    function jump_over_hurdle() {
        // suitable definition
    }

    function run_jump_or_finish () {
        if ( at_goal() ){
            // something
        } else if ( front_is_clear() ){
            // something
        } else {
            // something
        }
    }

    repeat(run_jump_or_finish, 42);

Note the structure of the ``if/else`` statements; as is mentioned above,
you should see that it gives three independent choices: only one of them
will be executed.

.. topic:: Do it!

    Write such a program and make sure it works.

Could this program work without changing anything for world **Hurdles 4**?
... Have a look and you will likely conclude that the answer is no.
You might want to try it just to be sure. It will take a little
``while`` until we are ready to write a program that can make Reeborg
race **Hurdles 4** as well as the other three.