Railroad Diagrams

-r compiles a grammar into a self-contained HTML page of railroad (syntax) diagrams, one per rule, using tabatkins/railroad-diagrams:

px -r px.px > px-grammar.html

Whitespace-only helper rules (like Px’s own s) clutter a diagram set without adding anything worth reading — each -x rulename excludes one rule:

px -r -x s -x space -x blankline px.px > px-grammar.html

The output is a <dl> of <dt> rule names next to a <dd> containing a <script> that draws that rule’s diagram — it needs railroad-diagrams.js and its stylesheet loaded on the page (this site vendors a copy under assets/, from strpp/scripts — CC0, by Tab Atkins Jr.; the generated HTML itself expects them at a relative ../scripts/ path, which you can adjust to wherever you keep a local copy).

Live, generated straight from px.px

This is the actual output of px -r px.px for four rules — a top-level rule, the scope_annotation it can carry, the six kinds of atom, and literal (notice the ![\'] terminal: that’s the stop-condition lookahead from pitfalls.md, drawn as a rail you can literally see the parser refusing to take).

Each diagram reads left to right along the main rail; a side loop is a repetition, a fork is a choice, and a labelled box that links elsewhere is a call to another rule — atom’s six side-by-side branches are the same six-way ordered choice from The Px Language, just drawn instead of tabulated.