Editing GNU Octave (section)

===Unwind-protect===
Octave supports a limited form of [[exception handling]] modelled after the [http://www.lispworks.com/documentation/HyperSpec/Body/s_unwind.htm <code>unwind_protect</code>] of [[Lisp (programming language)|Lisp]]. The general form of an unwind_protect block looks like this:
<syntaxhighlight lang="octave">
unwind_protect
   body
unwind_protect_cleanup
   cleanup
end_unwind_protect
</syntaxhighlight>

As a general rule, GNU Octave recognizes as termination of a given <code>''block''</code> either the keyword <code>end</code> (which is compatible with the MATLAB language) or a more specific keyword <code>end''block''</code> or, in some cases, <code>end_''block''</code>. As a consequence, an <code>unwind_protect</code> block can be terminated either with the keyword <code>end_unwind_protect</code> as in the example, or with the more portable keyword <code>end</code>.

The ''cleanup'' part of the block is always executed. In case an exception is raised by the ''body'' part, ''cleanup'' is executed immediately before propagating the exception outside the block <code>unwind_protect</code>.

GNU Octave also supports another form of exception handling (compatible with the MATLAB language):
<syntaxhighlight lang="matlab">
try
   body
catch
   exception_handling
end
</syntaxhighlight>

This latter form differs from an <code>unwind_protect</code> block in two ways. First, ''exception_handling'' is only executed when an exception is raised by ''body''. Second, after the execution of ''exception_handling'' the exception is not propagated outside the block (unless a <code>rethrow( lasterror )</code> statement is explicitly inserted within the ''exception_handling'' code).