About: This document specifies the Turtle Graphics language.
Version: 2017-Jun-01 19:12
Author: Pedro Izecksohn
Copyright: Public domain to be standardized.

Any document using the Turtle Graphics language to describe a drawing should
use .tg at the end of its file name.

Introduction:

  1) The screen measures 1 by 1.
  2) The decimal point is the . .
  3) In .tg files the angles must be in degrees.
  4) 90 degrees is down. 0 degrees is right.
  5) Turtle's initial angle is -90 degrees that is up.
  6) Turtle's initial coordinates are 0.5,0.5.
  7) All commands are composed by a single upper case letter or symbol.
  Some commands are followed by a space followed by an integer or by a 
  double precision number. Some commands are followed by a space followed by
  a string that continues until the line-feed character.

Commands:

A a
Set angle to a degrees.

T t
Turn the turtle t degrees.

X x
Set position.x to x.

Y y
Set position.y to y.

F n
Walks forward n.

U
Pen up. IOW: Stops of drawing.

D
Pen down. IOW: Restarts to draw. Also draws that pixel where the pen is.

R n
Repeats n times the next lines until E.

E
Ends a block started by R.

C c
Sets the color to c where c is an integer that fits in 8 bits. The default
color is 255.

# comment
Inserts the comment comment. Just the first comment is written in the PGM.

P p
Since version 005 the usage of P is deprecated.
On version 004 it sets the step_length of F to p. The default step_length is
 0.001.
On version 005 the step_length is automatically set for continuos lines.

B
Prints debugging information to stdout. The result of this command is 
implementation dependent.

Historic Information:

  The version 004 is the last version in Python written by Pedro Izecksohn.
  The version 005 is the first C version written by Pedro Izecksohn.
