// for single () iterates once when the expression is not null
// and zero times when it is null.
// It was actually used once.
svoid tok_for_single(LS tok) {
  int i = -1;
  while ((i = jfind(tok, i+1, "for single (")) >= 0) {
    int iColon = indexOf(tok, ":", i);
    int iClosing = findEndOfBracketPart(tok, iColon)-1;
    tok.set(iColon, ": singletonUnlessNull(");
    tok.set(iClosing, "))");
    clearTokens(tok, i+2, i+4);
    reTok(tok, i, iClosing+1);
  }
}

Began life as a copy of #1023091