Turtle Speak

Turtle speak or just ts is a dialect of the Logo programming language. It is offered as an alternative way of turtle scripting instead of directly using a turtle instance from jsr-223 scripts. Turtle scripts are very small, even complex scripts often fit on a single line.

Example

This simple script draws a square with a side length of 10 blocks:

rep 4 (fd 10 rt)

A slightly longer version:

repeat 4 (forward 10 right)

EBNF

Legend

• definition: foo := bar
• terminal string: "x" or 'x'
• range: alphabet := "a".."z"
• alternation: this | that
• option: [option]
• grouping: (group)
• repetition: {thisOccursZeroOrMoreTimes}
• exception: anyDigitButZero := digit -"0"
• special sequence: ? printable character ?

Version 0 (currently implemented)

Note: Everything is case insensitive unless stated otherwise.

whitespace  := ? whitespace character \s

ws          := whitespace {whitespace}

optional_ws := {whitespace}

digit       := "0".."9"
sign        := "+" | "-"

integer     := [ sign ] digit { digit }

float       := integer [ "." digit { digit } ]

argument    := integer | float

keyword     := "lt" | "left" | "rt" | "right" | "up" | "dn" | "down" |
				"fd" | "forward" | "bw" | "backward" | "pu" | "penup" |
				"pd" | "pendown" | "rep" | "repeat" |
				"goup" | "godn" | "godown" | "reset"

command     := keyword ws {argument} optional_ws [block]

block       := "(" optional_ws command {ws command} optional_ws ")"

program     := command ws {command}

Version 1

This version introduces string literals, variables and procedures as well as new commands.

character               := "A".."Z" | "_"

identifier              := character { character | digit}

quote                   := '"' -'\"'

string character        := ? any printable character ?

string                  := quote {string character -quote} quote

variable                := "$" identifier

argument                := integer | float | string | variable

procedure name          := identifier -keyword

procedure declaration   := "to" ws identifier ws {variable} optional_ws block

procedure call          := identifier {ws argument}

keyword+                := "block" | "bl"

comment                 := "//" {string character} ?line end?

The Future(tm)

Preprocessor?

Could be used to specify which turtle to use, cui arguments needed etc. to make ts scripts runnable without any additional scripting.

Logic & arithmetic expressions?

• logic operators: == != < > <= >= ! | &
• arithmetic operators: + - / * \ ^ ++ -- = += -= /= *=

Ideas:

• for prolonged sanity don't support complex expressions with parens or multiple operations, which would require correct operator precendence.
• when the analyser stumbles upon a literal or variable look ahead to see if the next token is an operator and handle that like a keyword
• prefix operators can be handle like a keyword: ++$x ==> plusplus $x
• the lexer must be modified to separate the tokens correctly: $x^2==> {"$x","^","2"}
• Dialects should define the operators just like they do with keywords already.
• repeat $foo * 2 ($i *= 1.2 fd $i rt $angle)
• if 0 == $x \ 2 (pd) else (pu)
• actually thats bad, use prefix notation: mod $isOdd $x 2 if $isOdd (foo)
• maybe even better, use blocks set $foo [add $a [sub $b $c]] // foo = a + (b - c) nah, that's complicated again.