GRAPHICS
========

The center of the graphics window is turtle location [0 0].  Positive
X is to the right; positive Y is up.  Headings (angles) are measured
in degrees clockwise from the positive Y axis.  (This differs from the
common mathematical convention of measuring angles counterclockwise
from the positive X axis.)  The turtle is represented as an isoceles
triangle; the actual turtle position is at the midpoint of the base
(the short side).


TURTLE MOTION
-------------

FORWARD dist
FD dist

	moves the turtle forward, in the direction that it's facing, by
	the specified distance (measured in turtle steps).

BACK dist
BK dist

	moves the turtle backward, i.e., exactly opposite to the
	direction that it's facing, by the specified distance.  (The
	heading of the turtle does not change.)

LEFT degrees
LT degrees

	turns the turtle counterclockwise by the specified angle,
	measured in degrees (1/360 of a circle).

RIGHT degrees
RT degrees

	turns the turtle clockwise by the specified angle, measured in
	degrees (1/360 of a circle).

CLEARSCREEN
CS

	erases the graphics window and sends the turtle to its initial
	position and heading.

HOME

	moves the turtle to the center of the screen.


PEN CONTROL
-----------

The turtle carries a pen that can draw pictures.  At any time the pen
can be UP (in which case moving the turtle does not change what's on
the graphics screen) or DOWN (in which case the turtle leaves a
trace).


PENDOWN
PD

	sets the pen's position to DOWN, without changing its mode.

PENUP
PU

	sets the pen's position to UP, without changing its mode.


SETPENCOLOR colornumber
SETPC colornumber

        sets the pen color to the given number, which must be a
        nonnegative integer. Color 0 is always black; color 7 is always
        white. Other colors may or may not be consistent between
        machines.


SETBACKGROUND color
SETBG color

        set the screen background color.



CONTROL STRUCTURES
==================

REPEAT num instructionlist

	command.  Runs the "instructionlist" repeatedly, "num" times.
        Example:  REPEAT 4 [FD 100 RT 90]

BYE

	command.  Exits from Logo; returns to the operating system.


WORKSPACE MANAGEMENT
====================

PROCEDURE DEFINITION
--------------------

TO procname :input1 :input2 ...				(special form)

	command.  Prepares Logo to accept a procedure definition.  The
	procedure will be named "procname" and there must not already
	be a procedure by that name.  The inputs will be called "input1"
	etc.  Any number of inputs are allowed, including none.  Names
	of procedures and inputs are case-insensitive.

	Unlike every other Logo procedure, TO takes as its inputs the
	actual words typed in the instruction line, as if they were
	all quoted, rather than the results of evaluating expressions
	to provide the inputs.  (That's what "special form" means.)

	Logo responds to the TO command by entering procedure definition
	mode.  The prompt character changes from "?" to ">" and whatever
	instructions you type become part of the definition until you
	type a line containing only the word END.

	Example:	TO SQUARE :SIZE
			REPEAT 4 [FD SIZE RT 90]
			END



WORKSPACE CONTROL
-----------------

SAVE filename

	command.  Saves the definitions of all unburied procedures,
	variables, and property lists in the named file.
        Example:  SAVE "I:/MA562/FRIEZES.TXT

LOAD filename

	command.  Reads instructions from the named file and executes
	them.  The file can include procedure definitions with TO, and
	these are accepted even if a procedure by the same name already
	exists.  If the file assigns a list value to a variable named
	STARTUP, then that list is run as an instructionlist after the
	file is loaded.
        Example:  LOAD "I:/MA562/FRIEZES.TXT