E4180

Compiler diagnostic name: unsupported_match_strategy.

Unsupported lexmatch match strategy.

lexmatch only supports the default first-match strategy and the explicit longest strategy. Other strategy names are rejected.

Warning

lexmatch is deprecated for new code. Prefer regex match expressions such as value =~ re"..." for boolean checks, or lexscan for case-based scanning.

Erroneous example

The following example asks for an unsupported shortest strategy:

///|
fn classify(input : String) -> String {
  lexmatch input with shortest {
    "if" => "keyword"
    _ => "identifier"
  }
}

///|
test {
  ignore(classify)
}

MoonBit will report an error.

Suggestion

Rewrite the code with a regex match expression when first-match behavior is enough, or use lexscan ... with longest for longest-match scanning:

///|
fn classify(input : String) -> String {
  if input =~ re"^if$" {
    "keyword"
  } else {
    "identifier"
  }
}

///|
test {
  inspect(classify("if"), content="keyword")
  inspect(classify("gift"), content="identifier")
}