E4171

Compiler diagnostic name: last_regex_case_must_be_catchall.

The last case in a lexmatch expression must be a catch-all pattern.

MoonBit checks lexmatch expressions for exhaustiveness. When all previous regex patterns fail, the expression still needs a final branch that can handle the remaining input.

Erroneous example

///|
pub fn match_text(text : String) -> Unit {
  lexmatch text with longest {
    "abc" => ()
  }
}

The only branch matches "abc", so other input has no branch to run.

Suggestion

Add a final _ case, or otherwise make the last case catch all remaining input.

///|
pub fn match_text(text : String) -> Unit {
  lexmatch text with longest {
    "abc" => ()
    _ => ()
  }
}