svoid tok_replaceColonEqualsSyntax(LS tok) {
  int i;
  
  // "field := value" for defining fields e.g. in "uniq"
  while ((i = jfind_check(":", tok, "<id> :=")) >= 0) {
    S id = tok.get(i);
    
    // special case for null := which we interpret as actually null,
    // not "null"
    
    S string = eq(id, "null") ? id : quote(id);
    tok.set(i, string);
    tok.set(i+2, ",");
    tok.set(i+4, "");
    reTok(tok, i, i+5);
  }
  
  // "quoted" := value
  while ((i = jfind_check(":", tok, "<quoted> :=")) >= 0) {
    tok.set(i+2, ",");
    tok.set(i+4, "");
    reTok(tok, i, i+5);
  }
  
  // <int> := value
  while ((i = jfind_check(":", tok, "<int> :=")) >= 0) {
    tok.set(i+2, ",");
    tok.set(i+4, "");
    reTok(tok, i, i+5);
  }
  
  // all other cases: just replace with comma
  jreplace(tok, ":=", ",");
}