ple,
</p>

<pre><code>for i 5 -1</code></pre>

<p>
causes the syntax error, because the second parameter is regarded as "5-1" instead of "5" and the third parameter is empty. To avoid this problem, take one of the following solutions:
</p>

<ol>
  <li>Put "0" before "-".
<pre><code>for i 5 0-1</code></pre>
  </li>

  <li>Add parentheses.
<pre><code>for i 5 (-1)</code></pre>
  </li>

  <li>Assign the negative constant to a variable.
<pre><code>
A = -1
for i 5 A
</code></pre>
  </li>
<