49. First-Character Dispatch in Generated Choices

• In generated parsers, an alternative of a choice that must begin with a given terminal (a literal or a character class, possibly behind sequences, captures, #atomic, - and calls of rules that are neither left-recursive nor Operators Rule) is skipped when the next character cannot start it, recording the expectation it would have recorded. Such an alternative fails at once without its terminal, so nothing else is observable; the calls it skips would only have set memo bookkeeping, and the skip is not taken when those calls would exceed the nesting limit. value = object / array / string / number / bool / null in JSON, for instance, no longer calls four rules to parse a number.
• Effect (min of 12 interleaved runs, Apple M3 Max): Parse JSON 9.1 → 7.9 ms (−13%), XML −10%, Minilang and Recovery −9%, Arith_OperatorsRule −6%, CSV −4%; ParseAST JSON 7.3 → 6.4 ms (−12%), XML −10%, Arith_OperatorsRule −11%; fewer bytes and allocations (fewer memo entries). Recognize uses the same code.