tree-sitter-motoko

A tree-sitter grammar for the Motoko programming language, and mo-fmt, the Motoko formatter built on it.

Why does this exist?

There is an existing grammar at https://github.com/polychromatist/tree-sitter-motoko

I wanted to re-familiarize myself with every corner of Motoko's syntax, so I decided to implement my own. The existing grammar suffers from a tree-sitter bug, which made it unsuitable for implementing parser based indentation in Emacs. This grammar works around that bug.

Additional differences:

• Doesn't require a custom scanner
• Covers some more recent syntax additions (parentheticals), and some of the weirder lexical productions
• Parses the moc 2.0 syntax next to the legacy forms: unparenthesized if/while/switch/for heads with braced bodies (including the whitespace rule that a glued (/[ extends the head while a spaced one starts a bare branch), optional ; between cases, paren-free case patterns, and ?? with an expression-position right-hand side
• Follows the compiler's grammar more closely by implementing parameterized expression productions.
• ~33% reduction in compiled output size
• Tested to successfully parse every .mo file in the compiler repository, as well as base