4.1. Grammar🔗

The grammar language is a strict subclass of the regular languages:

• concatenation and finite alternatives;

• optional items and the dedicated sign terminal;

• built-in digit, hexDigit, and bit runs with {n}, {lo,hi}, or + lengths;

• separated repetition such as rep H16 sepBy ":" {8}.

Triptych checks the complete nonterminal graph during elaboration. If it detects a cycle, for example A -> B -> A, it rejects the declaration and reports the cycle. This check enforces the current non-recursive boundary. With an acyclic graph and field boundaries fixed by grammar structure, Triptych can emit readable predicates, executable decoding, and their equivalence mechanically.