LOGOTRANSCODE.md

Transcoding LOGO to WorldTurtle

Coordinate systems

WorldTurtle and LOGO have differing coordinate systems.

In LOGO, North is at 0°, and the heading increments clockwise.

In WorldTurtle, East is at 0°, and the heading increments counter-clockwise.

Turtle Commands

LOGO	TurtleCommands
FORWARD X (or FD X)	forward X (or fd X)
BACK X (or BK X)	backward X (or bk X)
LEFT X (or LT X)	left X (or lt X)
RIGHT X (or RT X)	right X (or rt X)
PENDOWN (or PD)	setPenDown
PENUP (or PU)	setPenUp
SHOWTURTLE (or ST)	setVisible
HIDETURTLE (or ST)	setInvisible
SETPENSIZE [X Y]	setPenSize X
HOME	home
LABEL S	label S
WAIT x	wait X
SETXY X Y	goto (X, Y)
ARC A R	arc a r
SETX X	position >>= \(_, y) -> goto (X, y)
SETY Y	position >>= \(x, _) -> goto (x, Y)
POS	position
XCOR	fst <$> position
YCOR	snd <$> position
SETHEADING X (or SETH X)	setHeading X

World Commands

LOGO	WorldCommands
CLEARSCREEN (or CS)	clear
CLEARTEXT	N/A

Repetition

LOGO

In LOGO, repetition is done via lists such as:

REPEAT X [COMMAND1 COMMAND2 COMMAND3]

WorldTurtle

In WorldTurtle, repetition is performed on one TurtleCommand, which can be composed of other commands using the (>>) operator.

repeatFor X (command1 >> command2 >> command3)

You can also use do-notation to achieve the same effect:

repeatFor X $ do 
    command1
    command2
    command3

Procedures

LOGO

In LOGO, procedures are written between to/end statements.

TO SQUARE
REPEAT 4 [FD 100 RT 90]
END

WorldTurtle

In Haskell everything is a function; there is no special syntax for procedures. (But do remember that indentation is important!)

square = repeatFor 4 $ fd 100 >> rt 90

In do-notation:

square = do
    repeatFor 4 $ do
        fd 100
        rt 100

Note that in Haskell, types can be implicitly calculated by the compiler, it is good practice to write a type declaration:

square :: TurtleCommand () 
square = repeatFor 4 $ fd 100 >> rt 90

Arguments

Both LOGO and Haskell functions can take arguments which follow the declaration name.

LOGO

TO SQUARE :n
REPEAT 4 [FD :n RT 90]
END

WorldTurtle

square :: Float -> TurtleCommand () 
square n = repeatFor 4 $ fd n >> rt 90