Supported formats

Format family	Frontend ID	Files	Main strengths	Important boundary
Yacc / Bison / Lrama	yacc-family	Single	Precedence, actions, named references	Recovery can be lossy
BNF / EBNF	bnf	Single	Grouping, choice, repetition	First file only
ANTLR4	antlr4	Multi-file	Parser/lexer grammar, EBNF, imports	Target code is lossy
Menhir	menhir	Single	Classic rules, inline, parameterized symbols	Some attributes are unsupported
Peggy / PEG.js	peggy	Single	Ordered choice, predicates, scannerless	Actions are not retained

The matrix describes the frontend boundary, not a claim that all dialect extensions are lossless. A parser frontend may emit diagnostics for syntax it can recognize only partially. Always read diagnostics and capability fields with the metrics.

Frontend selection

Use gramin detect to inspect candidates, but pass --frontend when detection is ambiguous. The browser sandbox follows the same rule: Auto refuses a tie instead of silently selecting a frontend.

Format notes

• Yacc family covers POSIX Yacc, Bison, and Lrama constructs supported by the yacc frontend.
• BNF / EBNF represents grammar productions and EBNF sugar without pretending that every notation has the same semantics.
• ANTLR4 supports parser and lexer grammar boundaries and split grammar files.
• Menhir includes supported standard-library calls and reports unsupported extensions as diagnostics.
• Peggy / PEG.js preserves ordered-choice and scannerless capability context.

For exact syntax and lossiness, consult the frontend package README and the frontend protocol.