4.1Drawing a square🔗 i

First you need to define a list of turtle commands for drawing a square. We will name it square1. Actual drawing of the turtle image is done using draw function, the turtle command list is given as an argument to draw .

(define square1

(list (forward 100)

(turn-left 90)

(forward 100)

(turn-left 90)

(forward 100)

(turn-left 90)

(forward 100)))

4.2Drawing a square using repeat🔗 i

Since the command list for drawing a square has a repeating pattern, it is better to define it separately and use it repeatedly. We will name it side and we will repeat it 4 times using repeat .

4.3Drawing two squares in a same picture🔗 i

We can use a previously defined square and draw two of those in the same picture. We will define a list of commands move to move to a new location and changes the pen color before drawing the second square.

(define move

(list (pen-up )

(turn-right 90)

(forward 100)

(pen-down )

(change-color "red")))

(define two-squares

(list square1

move

square1))

4.4Drawing a square using a function🔗 i

To be able to draw squares with changing side lengths, we need to define a function, which we will name changing-square. We need also a helper function changing-side to draw sides with changing lengths. The variable x is the side length. Finally we call the new function changing-square with argument 30 (x=30).

(define (changing-sidex)

(list (forward x)

(turn-left 90)))

(define (changing-squarex)

(repeat 4(changing-sidex)))

4.5Drawing a square using coordinates🔗 i

You can draw a square also by ordering the turtle to go via some points in the coordinate plane using go-to commands. To get easier coordinates we change the place of the origin with set-origin command.

(define coordinate-square

(list (set-origin )

(go-to 1000)

(go-to 100100)

(go-to 0100)

(go-to 00)))

4.6Mirroring a square🔗 i

We can draw two square so that the second one is created by mirroring the first one using a pivot point. The pivot point is the location where the mirroring was turned on (mirron-x-on, mirron-y-on), in this example it is the starting point.

(define mirroring-square

(list (mirror-x-on )(mirror-y-on )

square1))

4.7Drawing a square using a stamper🔗 i

We can activate the stamper functionality using stamper-on command. Now the turtle will "stamp" the given image after each movement. Here we use a red circle as the stamp. You could also let the pen draw the line also (here is it taken up).

(define STAMP(circle 5"solid""red"))

(define stamper-square

(list (stamper-on STAMP)

(pen-up )

square1))

4.8Changing pen style and size🔗 i

You can change the style of the line using change-pen-style command and the width of the line using change-pen-size command.

Note! This doesn’t work in WeScheme.

(define special-pen-square

(list (change-pen-size 5)

(change-pen-style "dot")

square1))

4.9Drawing a line in a grid🔗 i

First we draw a background grid using set-bg-grid . We move to the origin using (go-to 00) and activate the stamper with a blue circle as the stamp. To get the stamps in the right coordinates we need to command the turtle using go-to multiple times. In this example the stamper is inactivated after four points .

(define line-with-grid

(list (set-bg-grid 2020"pink")

(pen-up )

(go-to 00)

(stamper-on (circle 5"solid""blue"))

(pen-down )

(go-to 4040)

(go-to 8080)

(go-to 120120)

(go-to 160160)

(stamper-off )

(go-to 500500)))

4.10Drawing a line with multiple stamps🔗 i

We move to origin using go-to-origin command and draw a line using a list of stamps.

(define STAMPS

(list (circle 10"solid""red")

(star 10"solid""blue")

(circle 10"solid""green")

(star 10"solid""yellow")

(circle 10"solid""black")))

(define line-with-stamps

(list (pen-up )

(go-to-origin )

(turn-right 45)

(stamper-on STAMPS)

(repeat 8(forward 50))))

4.11Changing background color, background image and animation size🔗 i

You can change the background color using change-bg-color color and you can put an additional image on top of it using set-bg-image . In the example we want to draw a picture with different dimensions so draw-custom is used (setting the drawing speed to zero will not affect the drawing speed).

(define square-over-bg

(list (change-bg-color "black")

(set-bg-image (circle 100"solid""gold"))

square1))

4.12A line with changing colors🔗 i

In this example we set the pen color to be a list of colors. Turtle will use each color one after another. The animation speed has been set to be slower (the last argument of draw-custom ). The turtle is also hidden during the first part of the animation.

(define COLORS

(list "red""blue""green""yellow""purple"))

(define color-line

(list (pen-up )

(go-to 00)

(turn-right 45)

(pen-down )

(change-color COLORS)

(change-pen-size 10)

(hide-turtle )

(repeat 8(forward 40))

(show-turtle )

(repeat 8(forward 40))))