1.4. What it is not🔗

Triptych is not a general parser generator. Its grammar tier has concatenation, finite alternation, optional items, three built-in token classes, and separated repetition, but no recursion or data-dependent field boundaries. JSON and length-prefixed payloads are out of scope. General Base64 is not yet expressible because the grammar has no user-defined character class or unseparated repetition of a nonterminal.

That narrowness is what buys full automation. Within the class, everything is generated and proven with zero obligations; at the boundary, escape hatches let the accepted language be any decidable predicate and the parsed value be any type, at the cost of a small manual contract. A later chapter maps the gradient in detail.