static bool ctxProcessIf(L<S> tok) {
  int i;
  if ((i = jfind(tok, "if (")) == 1) {
    int iEnd = findEndOfBracketPart(tok, i+2)-1;
    S cond = join(subList(tok, i+4, iEnd-1));
    bool yes = ctxEvalCondition(cond);
    assertEquals("{", tok.get(iEnd+2));
    int iEndYes = findEndOfBlock(tok, iEnd+2)-1;
    S yesCode = join(subList(tok, iEnd+4, iEndYes-1));
    int j = iEndYes+2;
    S noCode = "";
    if (eqGet(tok, iEndYes+2, "else")) {
      int iNo = iEndYes+4;
      assertEquals("{", tok.get(iNo));
      int iEndNo = findEndOfBlock(tok, iNo)-1;
      j = iEndNo+2;
      noCode = join(subList(tok, iNo+2, iEndNo-1));
    }
    replaceTokens_reTok(tok, i, j, yes ? yesCode : noCode);
    true;
  }
  false;
}

Began life as a copy of #1008911