% Homework: Structures and variants, part II
% COMP 50
% Fall 2013

This homework is due at 11:59PM on **Monday, September 30**.  
Submit them using the COMP 50 Handin button on DrRacket; the homework
is the `structures-ii` homework.

All the exercises should be done using the *Beginning Student
Language*.


Finger Exercises
----------------
For this homework I am recommending the *same* finger exercises as for
the "Structures\ I" homework:

  - In the First Edition *How to Design Programs*, Exercises 6.4.1,
    6.4.3, 6.5.1, 6.6.1 (but instead of a symbol for color, please use
    a string), 6.6.3, 7.1.1, 7.1.3, 7.2.1, 7.2.2, 7.5.1, 7.5.3

  - Develop data examples for the structure definitions in Exercise 6.4.1
    

  - Write a function that converts a GPS position (as you define it
    below) to English

Problems to submit
------------------

1.  While riding in his convertible with the top down, Professor Jacob
    is struck in the head by an errant baseball.  When he recovers, he
    decides to hire you to create an experiment designed to confirm
    the validity of [Fitts's
    Law](http://en.wikipedia.org/wiki/Fitts's_law), which you can look
    up on Wikipedia.

    Professor Jacob asks you to design a `big-bang` program that
    reacts to mouse clicks ("button-down" mouse events).  In case the
    experimental subject decides not to click the mouse, the
    experimenter must also be able to limit the number of seconds for
    which the program runs.

    The program should draw the first mouse click as a seven-pointed,
    solid green star.  At that point it should place a red circle at a
    random location on the canvas (display).  The radius of the circle
    should be chosen randomly between 2 and 20 pixels.

    The program should then wait either for time to expire or for the
    experimental subject to click *within* the red circle.

      - If time expires, the program should write a consoling message
        over the canvas.

      - If the experimental subject successfully clicks within the red
        circle, the program should display a congratulatory message
        that includes the time that elapsed between the initial mouse
        click and the successful mouse click.  Professor Jacob would
        really like to measure time to the nearest tenth of a second. 

    After the message is written, the program should return a
    structure containing the information relevant to an experiment on
    Fitts's Law.  (DrRacket will continue to display the final result
    on the screen.)  Professor Jacob is still feeling a little foggy
    from the effects of the baseball, so you will have to use the
    [Wikipedia page](http://en.wikipedia.org/wiki/Fitts's_law) to
    figure out what information to return and how to represent it.

    Use all of the design recipes above, plus a *wish list*.


    **Domain knowledge**: The Wikipedia page talks about a "device", a
    "target", and a "movement."  The device is not under your control
    and you can't measure any of its properties directly.  The
    "target" is the red circle you create and the starting point is
    the star.  You are able to gather data about these aspects of the
    problem. 

    **Domain knowledge**: You will need the `2hdtp/image` and
    `2htdp/universe` teachpacks.  In the second edition,
    read [Section 3.6 (Designing World
    Programs)](http://www.ccs.neu.edu/home/matthias/HtDP2e/part_one.html#%28part._.D.K._sec~3adesign-world%29), especially
    [Figure 10: Signatures for interaction
    functions](http://www.ccs.neu.edu/home/matthias/HtDP2e/part_one.html#%28counter._.D.K._%28figure._world-signatures%29%29). 
 
      - To understand how a program be limited to a given number of
        seconds, read the documentation for `on-tick`.

      - To understand how to respond to the mouse, read the first part
        of [Section 3.7 (A Note on Mice and
        Characters)](http://www.ccs.neu.edu/home/matthias/HtDP2e/part_one.html#%28part._.A_.Note_on_.Mice_and_.Characters%29)
        in the second edition.

Karma problems
--------------
A.  Write a program that is similar to the line-drawing program we
    talked about in lab, except that if the program is doing the red
    rubber-band thing, clicking the mouse should turn the rubber band
    into a black line and should instantly start a *new* rubber band
    anchored at the point of the mouse click.  The program should stop
    rubber-banding when the Esc key is pressed.

    This program will make it easy for you to draw figures with
    connected line segments.

A.  Run the Fitts's Law experiment multiple times in succession and
    use the results to estimate the characteristics of your device.