#### 2.2.6 Circles

Circle `objects` are specified by center position and radius, and are purely graphical with no electrical meaning. They can be drawn in different colors, and with various stroke and fill settings.

See Object color. See Object fill and stroke.

Function: circle? object

  Returns ‘`#t`’ if and only if object is a circle `object`.

Function: make-circle center radius [color]

  Creates and returns a new circle `object`. center is the position of the center of the new circle in the form `(x . y)`, and radius is the integer radius of the circle. If color is specified, it should be the integer color map index of the color with which to draw the circle. If color is not specified, the default circle color is used.

Function: set-circle! circle center radius [color]

  Sets the parameters of circle. The arguments are the same as to `make-circle`. Returns circle.

Function: circle-info circle

  Returns the parameters of circle as a list of the form:

      ((center-x . center-y) radius color)

Function: circle-center circle

  Returns the position of the center of circle as in the form `(x . y)`.

Function: circle-radius circle

  Returns the radius of circle as an integer.