Module regex/error

Typed error for std/regex pattern and flag compilation.

Regex.new is a pure fallible transform, so it reports failure as Result(Regex, RegexError) — never as a string (see .github/instructions/yo-design.instructions.md, "std error handling"). Every variant is matchable, and RegexError implements Error so it can also be thrown as an AnyError.

Positions are byte offsets into the pattern, recording where the parser stopped — not necessarily where the construct began.

Example

{ Regex, RegexError } :: import("std/regex");

match(
  Regex.new(`a{3,1}`),
  .Ok(re) => (),
  .Err(e) => match(
    e,
    .QuantifierOutOfOrder(min, max, pos) => println(`bad {${min},${max}}`),
    _ => println(e)
  )
);

Stability

unstable — the enum is EXHAUSTIVE by construction (derive(Error) matches the messages against the variants in declaration order, so a variant added, removed or reordered is a compile error), which is exactly what makes it unsafe to freeze while the engine is still growing. Every new syntax the parser learns to reject adds a variant, and a caller who matched all fourteen arms without a _ then fails to compile — so additions here are not additive in practice. Freezing waits on the parser's grammar settling, or on a documented "non-exhaustive, always write a _ arm" promise. The shape (one variant per fixable fault, byte offsets into the pattern, Error so it can travel as an AnyError) is settled and matches D1.