catch cancel

catch-cancel.sjs

// This does not work at all, for unknown reasons:
let catch = macro {
  case {
    try {
      $tryBody ...
    } $name ($exception:ident) {
      $catchBody ...
    }
  } => {
    return #{
      try {
        $tryBody ...
      } catch ($exception) {
        if (!$exception || !Object.prototype.hasOwnProperty.call($exception, "__throwCancel")) {
          $catchBody ...
        } else {
          throw $exception;
        }
      }
    }
  }
}

// This works, but also catches the case of class C { foo() {} catch(e) {} }:
let catch = macro {
  case {
    $name ($exception:ident) {
      $catchBody ...
    }
  } => {
    return #{
      catch ($exception) {
        if (!$exception || !Object.prototype.hasOwnProperty.call($exception, "__throwCancel")) {
          $catchBody ...
        } else {
          throw $exception;
        }
      }
    }
  }
}

typical-input.js

// Want to transform this:

try {
  a();
} catch (e) {
  b(e);
}

// Do NOT want to transform this:

class C {
  foo() {
  }
  catch(e) {
  }
}