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<h1 class="top">Transitional and Strict modes</h1>
<p>Since version 5.00, Camlp5 has been able to be installed in two
modes: the <em>transitional</em> mode and the <em>strict</em>
mode. When Camlp5 is installed, it works with one only of these
modes (the two modes contain indeed different definitions of some
interfaces and are incompatible with one another). The user must
choose in which mode he wants to use Camlp5.</p>
<p>This notion has been introduced to ensure backward compatibility of
the Camlp5 syntax tree, together with the usage of a new quotation
kit "<tt>q_ast.cmo</tt>", which allows to use Camlp5 syntax tree
quotations in user syntax (with all its possible extensions).</p>
<dl style="font-size:80%; font-style:oblique">
<dt>A short example of these syntax tree quotations:</dt>
<dd>
<p>If the syntax of the <a href="grammars.html">extensible
grammars</a> has been added, it is possible to write things
like:</p>
<pre>
<:expr< EXTEND a: [ [ c = d -> $e$ ] ]; END >>;
</pre>
<p>representing the syntax tree of this statement: this is not
possible with the classical quotation kit "<tt>q_MLast.cmo</tt>"
because all quotations must be there only
in <a href="revsynt.html">revised syntax</a> and without syntax
extensions.</p>
</dd>
</dl>
<p>Here are the differences between the two modes:</p>
<dl>
<dt>Transitional</dt>
<dd>
<dl>
<dt>Compatibility</dt>
<dd>The syntax tree is fully compatible with the previous
versions of Camlp5, no changes has to be done in the users'
programs.</dd>
<dt>Quotation kit "<tt>q_ast.cmo</tt>"</dt>
<dd>The antiquotations are not available: when used, a syntax
error message is displayed.</dd>
</dl>
</dd>
<dt>Strict</dt>
<dd>
<dl>
<dt>Compatibility</dt>
<dd>The syntax tree is different, users' programs may have to be
modified, but not necessarily.</dd>
<dt>Quotation kit "<tt>q_ast.cmo</tt>"</dt>
<dd>All antiquotations are available.</dd>
</dl>
</dd>
</dl>
<p>In strict mode, the programs have more chances to be compatible
with the previous versions if they use syntax tree quotations rather
than syntax tree nodes. A solution is therefore to change the
expressions and patterns using nodes into expressions and patterns
using quotations (which is backward compatible).</p>
<h2>Which mode is installed ?</h2>
<p>To determine the mode of an installed version of Camlp5, type:</p>
<pre>
camlp5 -pmode
</pre>
<h2>Selecting mode when compiling Camlp5</h2>
<p>When compiling Camlp5 from source, the mode must first be selected
at configuration time. The <em>configure</em> script must be run
with one of these options:</p>
<pre>
./configure -strict
./configure -transitional
</pre>
<p>The default is "transitional", i.e. without option, the sources are
compiled in transitional mode.</p>
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