OCamllex & Menhir Support¶

neocaml includes dedicated tree-sitter modes for OCamllex and Menhir files. neocaml-ocamllex-mode activates automatically for .mll files; neocaml-menhir-mode activates for .mly files. Both provide font-lock, indentation, and imenu.

Grammar Installation¶

Each mode requires its own tree-sitter grammar, separate from the main OCaml grammars. The modes will prompt you to install the grammar on first use, or you can install them manually:

M-x neocaml-ocamllex-install-grammar
M-x neocaml-menhir-install-grammar

With a prefix argument (C-u), these commands reinstall even if the grammar is already present.

Note

The OCamllex grammar requires tree-sitter ABI version 15+ (tree-sitter >= 0.25.0). If your Emacs was built against an older tree-sitter, you may need to update it. See Troubleshooting for details.

Language Injection¶

On Emacs 30+, embedded OCaml code inside { } action blocks gets full OCaml syntax highlighting via language injection. This applies to both OCamllex action blocks and Menhir action/header blocks (%{ %}).

Language injection activates automatically when both the mode's grammar and the OCaml grammar are installed. No configuration is needed.

Imenu¶

Both modes provide imenu entries for quick navigation:

OCamllex: indexes rules (lexer_entry nodes) and named regexps
Menhir: indexes rules (both old-style and new-style)

Configuration¶

Both modes have a single indentation customization variable:

;; OCamllex indentation (default: 2)
(setq neocaml-ocamllex-indent-offset 4)

;; Menhir indentation (default: 2)
(setq neocaml-menhir-indent-offset 4)