## LOGO Commands 1

Use the commands below to start drawing pictures on the computer with your LOGO turtle. The command descriptions were adapted from the Berkeley Logo User Manual, Copyright 1993 by the Regents of the University of California.

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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

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