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-turtle-examples)

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