+ towrite &gt;= len) failwith(\"write\");
              /* Perform the write */
              _res = write(fd, data + ofs, towrite);
              /* Validate the result */
              if (_res == -1) failwith(\"write\"); ");
</pre><p>Custom deallocation sequences are useful to free data structures
dynamically allocated and returned by the C function. For instance,
a C function <span class=machine><span class=font-tt>f</span></span> that returns a <span class=machine><span class=font-tt>malloc</span></spa