ITEC 380 2009fall ibarland

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hw04
handling lists
due Oct.07 (Wed) and Oct.12 (Mon)

On Oct.07 (Wed), turn in the code just for #1-#4, to be spot-checked. (The turn-in details shown after problem #4.) On Oct.12 (Mon), also turn in the entire assignment. Your name and the assignment-number must be in a comment at the start of the file.

The following problems deal with frogger. Follow all steps of the design recipe (from lect04c—recursive structs: and the design recipe and/or How to Design Programs. However, you do not need to provide test cases for functions which return images/scenes.

This of course builds on hw03; include your hw03 solution, but clearly mark¹ where the hw04 portion of your solution begins. You will lose substantial credit if your hw04-specific functions repeat code which is already part of your hw03 solution; you should just call those functions, instead. (E.g. move-trucks had better call move-truck.)

For readability, I recommend putting all named-constants (including images) at the end of your file (as in hw03-soln.ss, for example).

1. [2pts; 3-4 lines]
   Give a data definition for a list-of-trucks, examples of the data, and a template for any function which takes a list-of-trucks as input (Note that this template has to be in comments, since you don't even know what the return type would be.)
2. [2pts; code is template + ~3 words]
   Write the function move-trucks (note the plural “s”), which maps move-truck onto a list of trucks:

   ; move-trucks: list-of-trucks -> list-of-trucks ; Return a list of all the trucks, where each has been moved.

   Test cases are required, of course.
3. [2pts; code is template + ~3 words]
   Write the function trucks-handle-key, which takes in a list of trucks and a single key, and returns a new list of trucks where each truck has been updated by that key (as per truck-handle-key).
   Test cases are required, of course.
4. [2pts; code is template + 2-4 words]
   Write the function draw-trucks, which takes in a list of trucks and a scene, and returns a new scene with every truck in the list overlayed onto it.
   No test cases are required for this problem, since the creating the expected image in advance is non-trivial.

Submit a printout the above four problems by themselves (without the rest of hw03, without the truck structs themselves, etc.), to be spot-checked. On WebCT, turn in the entire running code as hw04-check.

5. [5pts] Go back and update your world struct so that it contains a list-of-trucks. Modify your examples of world structs, and the functions update-world, world-handle-key, and draw-world from the previous homework (including test cases²).
6. [3pts] Write the function truck-off-screen?, which returns whether or not a given truck is entirely off the size of the image you use in draw-world. (Hint: call overlap? from hw03.)
   Note that this function neither consumes nor returns images; however it may use numbers (or better: named constants) which are also used inside draw-world.
7. [3pts] Write the function

   ; remove-off-screen-trucks : list-of-trucks -> list-of-trucks ; Return a list containing only those trucks are not off-screen.

8. [3pts] Write the function replenish-truck : list-of-trucks -> list-of-trucks, which sometimes adds new trucks to the given list. You can use whatever criterion you like:
   • Adding one new truck if the list's length falls below some threshold.
     (You can call length : list -> number; we wrote “my-length” in class, but “length” is also built-in.)
   • Add “enough” new trucks if the list's length falls below some threshold.
     (We haven't exactly seen this in class, but between a helper-function and getting a data-defintion for (natural) numbers, this can follows the same approach used in class.)
   • Adding one new truck with some probability.
   Note that you can create new trucks with (somewhat) random attributes; see the built-in function random. In this case, you may not always be able to write check-expects, but do show the results of calling your function on different inputs. (If you can definitely predict the result for certain inputs -- e.g. when the list is already longer than some threshold -- then do use check-expect to test those types of inputs.)
9. [3pts] Modify update-princess so that she teleports to a random location, after being in the same spot long enough.
10. [5pts] Modify update-world so that it (a) moves trucks, then (b) removes trucks which are off the screen, and finally (c) replenishes trucks.
    Update test cases appropriately, as possible.
11. [3pts] Write a structure for representing a frog, followed by several examples of the data.
    Hint: Don't include an image in the structure. Instead, just include some way to indicate which way the frog is facing. I suggest using "left", "up", etc.; since these strings also happen to be key-presses, this will make for some convenient³ for frog-handle-key.
12. [5pts] Write the method frog-handle-key. Test cases required, of course.

    Hint: Use contains? from class to see if the key-press is one of the four valid directions.

13. [3pts] Write the method draw-frog : frog scene -> scene.
    No test cases needed for this function.

    I recommend having a helper-function get-frog-image : string -> image which, given a string(keypress) for a frog's direction, returns an appropriate image. You can write test-cases for this helper function.

    To rotate or scale an image::

    You can open image-functions.ss in a new DrScheme tab, (clicking "Evaluate" once), and then just use the interactions window to cut/paste your original image and call functions like rotate90 or scale, cut/pasting the result back into your program.

    Or you can use photoshop. Or you can embed image-functions.ss in your hw, and call the rotate/scale functions every time you want to use them.

14. [3pts] Add frogs to your world structure, updating world-handling functions as necessary.
15. [3pts] Write truck-hitting-frog? : truck frog -> boolean.
    You can use overlap? on the truck's and frog's “bounding box”.⁴ Note that this function neither consumes nor returns images; test cases are required.
16. [3pts] Write trucks-hitting-frog? : list-of-trucks frog -> boolean, which returns whether any truck in the list is hitting the given frog.
17. [3pts] Write game-over? : world -> boolean.
    (The game is over when the frog is hit by a truck, or the frog has reached the princess.)
    Note that you can add the clause [stop-when game-over?] to the call to big-bang, to stop the simulation.
18. [0pts] Bonus: adding sounds.

    The function play-sound will play a sound file. In order to use this function, your program must contain (require scheme/gui). (Some free sound files can be found at, say, mediacollege.com or partnersinrhyme.com; be sure to site your sources.)

    Playing a sound is a side-effect -- it changes the state of the world, but it doesn't return a value. When calling a function which has a side-effect, we often use begin. For example, the following expression evaluates to 14, but plays a sound as a side effect:

    (begin (play-sound "/Users/ibarland/Music/sounds/effects/beepbeep-01.wav") (+ 8 6))

    If you want to conditionally play a sound, you could write

    (begin (if some-condition (play-sound "/Users/ibarland/Music/sounds/effects/beepbeep-01.wav") 'some-garbage-return-value) (+ 8 6))

    But this is a bit odd, having to provide an answer for the 'false' case, when we know that value is only going to get thrown away. Instead, you can use when:

    (begin (when some-condition (play-sound "/Users/ibarland/Music/sounds/effects/beepbeep-01.wav")) (+ 8 6))

    You may only use begin and when in order to play sounds, in this assignment. For example, if you use a when expression as the body of, say, update-princess you'll get a function that runs, but doesn't always return a value⁵ (!). If you bump yourself up to advanced-student, you should understand when to (not) use when and begin.

(The last 7pts: for overall good code (well indented; not roundabout).)

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©2009, Ian Barland, Radford University Last modified 2010.Jan.18 (Mon)

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