Slightly off topic.  The article doesn&#x27;t call it out but there&#x27;s a lovely assembly hack here.  In:<p>bec 1f &#x2F; branch if no error<p><pre><code>   jsr r5,error &#x2F; error in file name

       &lt;Input not found\n\0&gt;; .even

   sys exit
</code></pre>
jsr calls a subroutine passing the return address in register 5.  The routine error interprets the return address as a pointer to the string.<p>r5 is incremented in a loop, outputing one character at a time.   When the null is found, it&#x27;s time to return.<p>The instructions used to return from &quot;error:&quot; aren&#x27;t shown but there is a subtlety here, I think.<p>&quot;.even&quot; after the string constant assures that the next instruction, &quot;sys exit&quot;, to which &quot;error:&quot; is supposed to return, is aligned on an even address.<p>By implication, the return sequence in &quot;error:&quot; just be sure to increment r5, if r5 is odd.   I am guessing something like the pseudo-code:<p>inc r5<p>and r5, fffe<p>ret r5