static IF1 toIF1(fO f) {
  if (f == null) null;
  if (f instanceof IF1) ret (IF1) f;
  if (isString(f)) {
    ifndef callF_legacy
      fail("callF_legacy");
    endifndef
    ifdef callF_legacy
      ret mainFunctionToIF1((S) f);
    endifdef
  }
  ret new IF1 {
    public O get(O a) { ret callF(f, a); }
  };
}

Began life as a copy of #1011035