LOGO

LOGO:Turtle Graphics was an early CLI driven piece of 2D graphics software. The idea was that a turtle with a pen strapped to it could be instructed to do simple things like move forward 100 spaces or turn around. From these building blocks you could draw more complex shapes like squares, triangles, circles - using these to draw houses or sail boats. You could give titles to groups of instructions; essentially creating libraries of more complex commands. It was a simple and popular educational language for school children during the 80s to teach basic programming concepts.

FORWARD 100
LEFT 90
FORWARD 100
LEFT 90
FORWARD 100
LEFT 90
FORWARD 100

This would draw a square with sides 100 units long.

Rather than entering each line many versions of LOGO allowed you to put them all on the same line: "FORWARD 100 LEFT 90 FORWARD 100 LEFT 90 FORWARD 100 LEFT 90 FORWARD 100" was a valid command.

FORWARD 100
RIGHT 60
FORWARD 100
RIGHT 60
FORWARD 100

Would draw a triangle.

The turtle's pen could be lifted and lowered; drawing a dotted line was rudimentary. In this example we'll use the the shorthand for FORWARD, which is FD.

FD 10 (drawing a line and moving)
PENUP (now we've lifted the pen so it won't draw anything even if we do move)
FD 10 (not drawing but moving)
PENDOWN (now we've lowered the pen so it draws a line wherever the turtle moves)
FD 10 (drawing a line and moving)
PENUP
FD 10 (etc...)
PENDOWN
FD 10

You could loop (repeat) commands. This would draw the exact same box in the first example:

REPEAT 4 [FD 100 RIGHT 90]

Which would execute the command "FD 100 RIGHT 90" four times.

A simplistic circle consists of 360 individual rotations, each with a step forward, so "REPEAT 360 [FD 1 RIGHT 1]" would have the expected result.

You could title groups of instructions, ie. make procedures. These needed to be done from the Editor, and the command was Ed.

ED (to enter the editor mode, then the actual procedure)

TO BOBSAGET
REPEAT 4 [FD 100 RT 90]
FD 30
END