Thoughts on a syntax for a scripting language.md

Thoughts on a syntax for a scripting language

This document provides some basic ideas about how a syntax for specifying an L-system could look like.

Symbols

The only special symbols are:

• @ announces the definition of a symbol rather than a rule
• $ followed by a name, represents a basic literal for manipulating the cursor
• ( and ) are used to enclose arguments passed to basic literals
• ; ends a statement
• = initiates the substitutes for a symbol definition or a rule
• # begins a line comment

The allowed symbols between parentheses are:

• , to separate arguments
• -+0123456789. the argument itself should always be a number

The following symbols are always ignored:

• whitespaces
• non-printable characters

The available basic literals are (as in lsys.js):

• $rot
• $randomrot
• $draw
• $draw
• $move
• $move
• $thick
• $relthick
• $save
• $restore

Syntax

Any non-special symbol can be used as literal. The symbols that are used (in both definitions and rules) must be prefix-free, that is, for each pair of literals, no literal must be a prefix of the other one.

For instance, the following sets are disallowed:

• {F, F1, F_xy}
• {abc, abcde, xyz}

Whereas these are allowed:

• {F1, F2, F3}
• {abc, bc, c}
• {111, 110, 100}

Symbols are defined using the "@ literal = subst1 subst2 subst3 ...;" pattern. For example:

• @ > = $draw(1);
• @ :< = $move(-1);
• @ + = $rot(20);
• @ * = $relthick(1.25); Each symbol can only be defined once.

For rules, the @ modifier is dropped. For example:

• F = FFF>F;
• F = AA $save() B $rot(30) A]A;

Further thoughts

• Maybe introduce a $rand(a,b) function to generate a random number which can be used as an argument?
• Allow basic math operators like +, * etc. inside arguments (only!)
• Make parentheses optional if a basic literal does not expect any parameters