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turn/ radians
2.1 Examples

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    
  init-angle])  turtles?
  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).

(turtles? v)  boolean?
  v : any/c
Determines if v is a turtles drawing.

(move n turtles)  turtles?
  n : real?
  turtles : turtles?
Moves the turtle n pixels, returning a new turtles window.

(draw n turtles)  turtles?
  n : real?
  turtles : turtles?
Moves the turtle n pixels and draws a line along the path, returning a new turtles window.

(erase n turtles)  turtles?
  n : real?
  turtles : turtles?
Moves the turtle n pixels and erases a line along the path, returning a new turtles window.

(move-offset h v turtles)  turtles?
  h : real?
  v : real?
  turtles : turtles?
(draw-offset h v turtles)  turtles?
  h : real?
  v : real?
  turtles : turtles?
(erase-offset h v turtles)  turtles?
  h : real?
  v : real?
  turtles : turtles?
Like move, draw, and erase, but using a horizontal and vertical offset from the turtle’s current position.

(turn theta turtles)  turtles?
  theta : real?
  turtles : turtles?
Turns the turtle theta degrees counter-clockwise, returning a new turtles window.

(turn/radians theta turtles)  turtles?
  theta : real?
  turtles : turtles?
Turns the turtle theta radians counter-clockwise, returning a new turtles window.

(merge turtles1 turtles2)  turtles?
  turtles1 : turtles?
  turtles2 : turtles?
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.

(clean turtles)  turtles?
  turtles : turtles?
Produces a turtles like turtles, but with only a single turtle, positioned in the center.

2.1 Examples

 (require graphics/value-turtles-examples)

The graphics/turtle-examples library’s source is meant to be read, but it also exports the following examples.

(radial-turtles n turtles)  turtles?
  n : exact-nonnegative-integer?
  turtles : turtles?
Places 2n turtles spaced evenly pointing radially outward.

(spaced-turtles n turtles)  turtles?
  n : exact-nonnegative-integer?
  turtles : turtles?
Places 2n turtles evenly spaced in a line and pointing in the same direction as the original turtle.

(neato turtles)  turtles?
  turtles : turtles?
As the name says...

(regular-poly sides radius turtles)  turtles?
  sides : exact-nonnegative-integer?
  radius : real?
  turtles : turtles?
Draws a regular poly centered at the turtle with sides sides and with radius radius.

(regular-polys n s turtles)  turtles?
  n : exact-nonnegative-integer?
  s : any/c
  turtles : turtles?
Draws n regular polys each with n sides centered at the turtle.

(spokes turtles)  turtles?
  turtles : turtles?
Draws some spokes, using radial-turtles and spaced-turtles.

(spyro-gyra turtles)  turtles?
  turtles : turtles?
Draws a spyro-grya reminiscent shape.