> For the complete documentation index, see [llms.txt](https://www.lisppad.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.lisppad.app/libraries/lispkit/lispkit-draw-turtle.md).
# (lispkit draw turtle)
Library `(lispkit draw turtle)` defines a simple "turtle graphics" API. The API provides functionality for creating turtles and for moving turtles on a plane generating *drawings* as a side-effect. A *drawing* is a data structure defined by library `(lispkit draw)`.
A *turtle* is defined in terms of the following components:
* A position *(x, y)* defining the coordinates where the turtle is currently located within a coordinate system defined by parameters used to create the turtle via `make-turtle`
* A heading *angle* which defines the direction in degrees into which the turtle is moving
* A boolean flag *pen down* which, if set to `#t`, will make the turtle draw lines on the graphics plane when moving.
* A *line width* defining the width of lines drawn by the turtle
* A *color* defining the color of lines drawn by the turtle
* A *drawing* which records the moves of the turtle while the pen is down.
Turtles are mutable objects created via `make-turtle`. The functions listed below change the state of a turtle. In particular, they generate a drawing as a side-effect which can be accessed via `turtle-drawing`. For most functions, the turtle is an optional argument. If it is not provided, the function applies to the turtle provided by the `current-turtle` parammeter object.
**current-turtle** 
Defines the *current turtle*, which is used as a default by all functions for which the turtle argument is optional. If there is no current turtle, this parameter is set to `#f`.
**(turtle? *****obj*****)** 
Returns `#t` if *obj* is a turtle. Otherwise, it returns `#f`.
**(make-turtle *****x y scale*****)**
Returns a new turtle object. *x* and *y* determine the "home point" of the turtle. This is equivalent to the zero point of the coordinate system in which the turtle navigates. *scale* is a scaling factor.
**(turtle-drawing *****turtle*****)**
Returns the drawing associated with the given *turtle*.
**(turtle-x *****turtle*****)**
Returns the x coordinate of the position of the given *turtle*.
**(turtle-y *****turtle*****)**
Returns the y coordinate of the position of the given *turtle*.
**(turtle-angle *****turtle*****)**
Returns the current angle of the given *turtle*.
**(turtle-angle *****turtle*****)**
Returns the current angle of the given *turtle*.
**(turtle-pen-down? *****turtle*****)**
Returns `#t` if the given *turtle* has its pen down; otherwise `#f` is returned.
**(pen-up)** \
\&#xNAN;**(pen-up *****turtle*****)**
Lifts *turtle* from the plane. If *turtle* is not provided, the turtle defined by `current-turtle` is used. Subsequent `forward` and `backward` operations don't lead to lines being drawn. Only the current coordinates are getting updated.
**(pen-down)** \
\&#xNAN;**(pen-down *****turtle*****)**
Drops *turtle* onto the plane. If *turtle* is not provided, the turtle defined by `current-turtle` is used. Subsequent `forward` and `backward` operations will lead to lines being drawn.
**(pen-color *****color*****)** \
\&#xNAN;**(pen-color *****color turtle*****)**
Sets the drawing color of *turtle* to *color*. If *turtle* is not provided, the turtle defined by `current-turtle` is used. *color* is a color object as defined by library `(lispkit draw)`.
**(pen-size *****size*****)** \
\&#xNAN;**(pen-size *****size turtle*****)**
Sets the pen size of *turtle* to *size*. If *turtle* is not provided, the turtle defined by `current-turtle` is used. The pen size corresponds to the width of lines drawn by `forward` and `backward`.
**(home)** \
\&#xNAN;**(home *****turtle*****)**
Moves *turtle* to its home position. If *turtle* is not provided, the turtle defined by `current-turtle` is used.
**(move *****x y*****)** \
\&#xNAN;**(move *****x y turtle*****)**
Moves *turtle* to the position described by the coordinates *x* and *y*. If *turtle* is not provided, the turtle defined by `current-turtle` is used.
**(heading *****angle*****)** \
\&#xNAN;**(heading *****angle turtle*****)**
Sets the heading of *turtle* to *angle*. If *turtle* is not provided, the turtle defined by `current-turtle` is used. *angle* is expressed in terms of degrees.
**(turn *****angle*****)** \
\&#xNAN;**(turn *****angle turtle*****)**
Adjusts the heading of *turtle* by *angle* degrees. If *turtle* is not provided, the turtle defined by `current-turtle` is used.
**(right *****angle*****)** \
\&#xNAN;**(right *****angle turtle*****)**
Adjusts the heading of *turtle* by *angle* degrees. If *turtle* is not provided, the turtle defined by `current-turtle` is used.
**(left *****angle*****)** \
\&#xNAN;**(left *****angle turtle*****)**
Adjusts the heading of *turtle* by *-angle* degrees. If *turtle* is not provided, the turtle defined by `current-turtle` is used.
**(forward *****distance*****)** \
\&#xNAN;**(forward *****distance turtle*****)**
Moves *turtle* forward by *distance* units drawing a line if the pen is down. If *turtle* is not provided, the turtle defined by `current-turtle` is used.
**(backward *****distance*****)** \
\&#xNAN;**(backward *****distance turtle*****)**
Moves *turtle* backward by *distance* units drawing a line if the pen is down. If *turtle* is not provided, the turtle defined by `current-turtle` is used.
**(arc *****angle radius*****)** \
\&#xNAN;**(arc *****angle radius turtle*****)**
Turns the turtle by the given *angle* (in radians) and draws an arc with *radius* around the current turtle position if the pen is down. If *turtle* is not provided, the turtle defined by `current-turtle` is used.