Dragon Logo: learning to program with a turtle

Starting

Put the cartridge in with the computer switched off, then switch on. You see LOGO:, and that is the menu: press one letter, without ENTER.

R	Run mode: the screen for the turtle, and three lines for commands at the bottom
E	The editor: this is where you write procedures
S, T, ENTER	Save all procedures to tape
L, T, ENTER	Load from tape
P	Print on a printer
BREAK	From any mode: back to LOGO:

First steps

Press R and type one command per line, with a space before the number, then ENTER. FD 40 moves the turtle 40 steps forward, and RT 90 turns it right a quarter turn.

FD / BK	Forward / back
RT / LT	Turn right / left, in degrees
PU / PD	Pen up / pen down
HOME	Back to the middle, facing up
CLEAR	Clears the screen
HT / ST	Hide / show the turtle
PC 0–3	Pen colour
BG 0–3	Background colour

A first procedure

A procedure is a new word you teach the turtle. Press BREAK, then E, and type:

TO SQUARE
REPEAT 4 (FD 30 RT 90)
END
TO FLOWER :N
REPEAT :N (SQUARE RT 360/:N)
END

Press BREAK, then R, and type FLOWER 12. The turtle draws 12 squares around the middle, like a flower. :N is a number you hand to the procedure.

What is different from other Logos

• Round brackets. REPEAT 4 (FD 30 RT 90), not the square brackets most Logos use.
• REPEAT only inside a procedure. Run mode takes only simple commands, one per line. Loops and conditions go in the editor.
• A space after every word. FD40 with no space says the turtle does not know that word. Any key carries on.
• Whole numbers only. No fractions and no lists. Instead you get several turtles at once, and a DOODLE mode for small children: press @ in run mode and draw with the number keys.
• A circle. REPEAT 36 (FD 6 RT 10) inside a procedure gives a good circle.
• Keep out of the bottom lines. A turtle that wanders into the three command lines gets smeared when the text scrolls.

This guide is in our own words, for Dragon owners who have the original program. We do not host the program or its original manual. We tried every step on an emulated machine with the same chips.