▼ |  | Turtle Graphics

1 | Traditional Turtles
2 | Value Turtles

► | 2 | Value Turtles

2.1 | Examples

On this page:

turtles
move
draw
erase
move-offset
draw-offset
erase-offset
turn
turn/ radians
merge
2.1`` Examples

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### 2`` Value Turtles

( require graphics/value-turtles )

The value turtles are a variation on traditional turtles. Rather than having just a single window where each operation changes the state of that window, in the graphics/value-turtles library, the entire turtles window is treated as a value. This means that each of the primitive operations accepts, in addition to the usual arguments, a turtles-window value; instead of returning nothing, each returns a turtles-window value.

( turtles |  | width |  |  |  |
|  | height |  |  |  |
| [ | init-x |  |  |  |
|  | init-y |  |  |  |
|  | init-angle]) |  | → |  | turtles-window?

width : real?
height : real?
init-x : real? = ( / width 2)
init-y : real? = ( / height 2)
init-angle : real? = 0

Creates a new turtles window with the given width and height. The remaining arguments specify position of the initial turtle and the direction in radians (where 0 is to the right).

( move n turtles) → turtles-window?
n : real?
turtles : turtles-window?

Moves the turtle n pixels, returning a new turtles window.

( draw n turtles) → turtles-window?
n : real?
turtles : turtles-window?

Moves the turtle n pixels and draws a line along the path, returning a new turtles window.

(erase n turtles) → turtles-window?
n : real?
turtles : turtles-window?

Moves the turtle n pixels and erases a line along the path, returning a new turtles window.

(move-offset h v turtles) → turtles-window?
h : real?
v : real?
turtles : turtles-window?

(draw-offset h v turtles) → turtles-window?
h : real?
v : real?
turtles : turtles-window?

(erase-offset h v turtles) → turtles-window?
h : real?
v : real?
turtles : turtles-window?

Like move, draw, and erase, but using a horizontal and vertical offset from the turtle’s current position.

( turn theta turtles) → turtles-window?
theta : real?
turtles : turtles-window?

Turns the turtle theta degrees counter-clockwise, returning a new turtles window.

( turn/radians theta turtles) → turtles-window?
theta : real?
turtles : turtles-window?

Turns the turtle theta radians counter-clockwise, returning a new turtles window.

( merge turtles1 turtles2) → turtles-window?
turtles1 : turtles-window?
turtles2 : turtles-window?

The split and tprompt forms provided by graphics/turtles isn’t needed for graphics/value-turtles, since the turtles window is a value.

Instead, the merge accepts two turtles windows and combines the state of the two turtles windows into a single window. The new window contains all of the turtles of the previous two windows, but only the line drawings of the first turtles argument.

#### 2.1`` Examples

( require graphics/value-turtles-examples )

The graphics/value-turtles-examples library is similar to graphics/turtle-examples, but using graphics/value-turtles instead of graphics/turtles.

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