Pop-11 gets a tree-sitter grammar — and a Zed extension to go with it

Having revived Poplog on modern silicon, we ran into the next problem: forty years of Pop-11 source, and no editor on earth that knows what it is looking at. So we wrote the grammar — tree-sitter-pop11 — and then the extension that consumes it, zed-pop11.

Parsing a language that redefines its own syntax

Pop-11’s syntax is user-extensible: a program can define new syntax words at compile time. No static grammar can ever be complete, so the design goal was never completeness — it was graceful degradation. This grammar parses the stable core faithfully and lets everything else fall back to a flat item “soup” rather than derailing the whole file.

The core it does handle is not small:

• Comments (;;; … and nesting /* … */), strings, word literals in closed, """ and unclosed "ml] forms, character constants in every historical spelling including the legacy unclosed `7, and radix numbers like 16:FF.
• define/enddefine in all its shapes — modifiers, :forms, infix operator definitions, the = expr value form — with the defined name captured for highlighting.
• The closed set of core block syntax words and their end… closers, including the archaic until … then … enduntil loop.
• Declarations (vars, lvars, dlocal, constant, procedure typing, syntax-word name lists), uses in its bare, parenthesised and hyphenated forms, exload blocks, and vedset key maps where [ is a literal token.
• Quoting semantics — [ … ] and { … } quote their contents so any keyword inside is data, while % … % switches back to evaluation.
• The #_IF family of compile-time directives and #_< … >_#.

Measured against the real thing

The grammar was validated against the full Poplog tree — 1,805 files, 270,000 lines spanning 1985 to 2026, including the syspop system dialect and the internals of the Lisp, Prolog and ML subsystems. 95.2% of files parse without errors, and the user-facing library corpus plus every modern library parse clean.

In the editor

zed-pop11 brings that to Zed: highlighting, outline symbols, folding, brackets and comment support for .p, .ph and .pop11 files. It’s in the Zed extension registry — search “Pop-11” in zed: extensions.

One honest caveat, documented in the README: .p is contested. Pascal, Gnuplot and OpenEdge all claim it, and Zed has no content sniffing. The extension takes .p; if that’s wrong for your project, override it per-project in .zed/settings.json.

Both MIT. This is phase P1 of the Poplog editor-bindings plan — the Pop-11 LSP server (real-compiler diagnostics, HELP hover, dictionary completion) already ships in the poplog repo, and wiring it to Zed is the next step.