E4172

Compiler diagnostic name: invalid_regex_pattern.

Invalid regex pattern.

This error happens when a re"..." literal or a regex pattern used by lexmatch does not follow MoonBit's regex syntax. Regex literals are checked at compile time, so syntax errors, unsupported assertions, invalid ranges, and duplicate capture names are reported before the program runs.

Erroneous example

fn invalid_regex() -> Regex {
  re"[a-z"
}

The character class starts with [, but never closes with ].

Suggestion

Fix the regex syntax, or rewrite the pattern using a supported regex form.

fn valid_regex() -> Regex {
  re"[a-z]"
}