# Making and Manipulating Lists of Drawings

Summary: In this laboratory, you will experiment with ways to build and use lists of drawings.

## Preparation

a. Make a copy of `lists-of-drawings-lab.scm`, which contains some useful code for this lab.

b. Make a list (mental, on paper, or on the computer) of the procedures and values initially included in the file.

c. In your own words, explain the difference between `check-drawing` and `check-drawings`.

## Exercises

### Exercise 1: Some Simple Drawings

Create each of the following drawings.

a. `sample-circle`, a circle of diameter 5, centered at (0,50).

b. `sample-square`, a square of edge-length 4, centered at (0,25).

### Exercise 2: Making Lists

a. The reading claims that we can make a list of drawings with ```(list drawing1 ... drawingn)```. Make and render a list of the two drawings you created in the previous exercise.

b. The reading claims that we can make a list of identical drawings with the `make-list` procedure, as in the following.

````>` `(make-list 5 "Hello")`
```

Verify this claim.

c. Create a value, `ten-circles`, that consists of 10 copies of `sample-circle`.

d. Have the Scheme interpreter print out that value to see whether it seems to contain the expected ten copies.

e. What do you expect to have happen when we try to render `ten-circles` with `check-drawings`?

````>` `(check-drawings ten-circles)`
```

You may find it useful to look at the notes on this exercise.

### Exercise 3: Shifting Drawings

As you may recall, `(map drawing-hshift list-of-drawings list-of-offsets)` builds a new list of drawings by horizontally shifting each element of `list-of-drawings` by the corresponding elements of `list-of-offsets`.

Consider the following sequence of instructions:

```(define list01 (list 0 10 20 30 40 50 60 70 80 90))
(define list02 (list 10 25 33 45 60 100 110 111 112 120))
(define ten-circles-01 (map drawing-hshift ten-circles list01))
(define ten-circles-02 (map drawing-hshift ten-circles list02))
(define ten-circles-03 (map drawing-vshift ten-circles list01))
(define ten-circles-04 (map drawing-vshift ten-circles list02))
(define ten-circles-05 (map drawing-vshift ten-circles-02 list01))
(define ten-circles-06 (map drawing-hshift ten-circles-01 list01))
```

a. Where do you expect the circles in each list to fall?

````>` `(check-drawings ten-circles-01)`
`>` `(check-drawings ten-circles-02)`
`>` `(check-drawings ten-circles-03)`
`>` `(check-drawings ten-circles-04)`
`>` `(check-drawings ten-circles-05)`
`>` `(check-drawings ten-circles-06)`
```

### Exercise 4: Systematically Shifting Lists of Drawings

a. As you may recall, `(iota n)` makes a list of the numbers from 0 to `n`-1. Predict what `(iota 10)` is and check your answer experimentally.

b. What do you expect the result of the following to be?

````>` ```(check-drawings (map drawing-hshift
(make-list 50 sample-square)
(iota 50)))```
```

c. What do you expect the result of the following to be?

````>` ```(check-drawings (map drawing-hshift
(map drawing-vshift
(make-list 50 sample-square)
(iota 50))
(iota 50)))```
```

d. What do you expect the result of the following to be?

````>` ```(check-drawings (map drawing-hshift
(map drawing-vshift
(make-list 50 sample-square)
(reverse (iota 50)))
(iota 50)))```
```

e. What do you expect the result of the following to be? (You need not specify all the members of each list; just summarize.)

````>` `(map mod7 (iota 50))`
`>` `(map times5 (iota 50))`
`>` `(map times5 (map mod7 (iota 50)))`
`>` `(map mod7 (map times5 (iota 50)))`
```

f. What do you expect to get for each of the following?

````>` ```(check-drawings (map drawing-hshift
(map drawing-vshift
(make-list 50 sample-square)
(map mod7 (iota 50)))
(map times5 (iota 50))))```
`>` ```(check-drawings (map drawing-hshift
(map drawing-vshift
(make-list 50 sample-square)
(map times5 (map mod7 (iota 50))))
(map times5 (iota 50))))```
```

### Exercise 5: Systematic Shifting, Continued

In the final stages of the previous exercise, we got a series of diagonals built by replicating an image. But what if we wanted something more “v-shaped”?

a. Let's start with a simple v. Using an appropriate combination of `iota`, `reverse`, `append`, `map`, and `increment`, create the list `(0 1 2 3 ... 24 25 24 23 ... 3 2 1)` and call it `vee`.

Hint: Try to think about how you systematically build the two halves of that list (the numbers in increasing order and then the numbers in decreasing order).

b. Using the list `vee`, as well as `(iota 50)`, build a “V-shaped” sequence of circles called `vee-circles`.

c. Using the list `vee`, as well as `(iota 50)`, build a “>-shaped” sequence of squares `vee-squares`.

### Exercise 6: Recoloring Drawings

Take any of your lists of fifty shapes from the previous exercises and arrange so that the first 10 shapes are colored blue, the next 15 are colored red, and the last 25 are colored green.

It is likely that you'll want to take two steps to this: First, build a list of 10 copies of blue, 15 copies of red, and 25 copies of green. (You can use `make-list` and `append`.) Second, use `map` and `drawing-recolor` to recolor the individual drawings.

### Exercise 7: Systematically Scaling Lists of Drawings

Here is a rendering of a simple diagonal of unit squares.

````>` ```(check-drawings (map drawing-hshift
(map drawing-vshift
(make-list 50 drawing-unit-square)
(map times5 (iota 50)))
(map times5 (iota 50))))```
```

a. Update that sequence of drawings so that the squares range systematically in edge length from 1 to 5. (That is the lengths will be 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, ....) You'll need to build the list of lengths and then use `map` to change the size of the squares.

b. Update the first sequence of drawings so that the width of the rectangles ranges systematically from 1 to 5, but the height stays 1.

c. Update the first recent sequence of drawings so that the width of the rectangles ranges systematically from 1 to 5 and the height of the rectangles ranges systematically from 1 to 7.

## Explorations

You have now learned how to systematically shift, scale, and recolor copies of a single drawing. Put these different techniques together to create the most interesting drawing you can.

## Notes on the Exercises

### Notes on Exercise 2

For part f, since all of the drawings are in the same place, rendering the list of drawings will produce the same result as rendering just one of the drawings.

Copyright (c) 2007-9 Janet Davis, Matthew Kluber, Samuel A. Rebelsky, and Jerod Weinman. (Selected materials copyright by John David Stone and Henry Walker and used by permission.)

This material is based upon work partially supported by the National Science Foundation under Grant No. CCLI-0633090. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License. To view a copy of this license, visit `http://creativecommons.org/licenses/by-nc/2.5/` or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.