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<title>Directives</title>
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<h1 class="top">Directives</h1>
<p>Directives in normal or revised syntax are statements at top level,
or, more generally, as signature items or structure items, which
stops the preprocessor for evaluate things - which can change the
behaviour of the preprocessor, for example to add syntax, load
syntax extensions and so on. After the directive is evaluated,
the parsing resumes.</p>
<p>Directives begin with '#', followed by an identifier, and,
optionnally by an expression. They are usable in source files the
and generally in the ocaml toplevel too.</p>
<p>Four predefined directives exist: #load, #directory, #option and
#use. It is also possible to add other directives. An example of
that is the parsing kit <a href="pragma.html">pa_pragma.cmo</a>
which adds a new directive #pragma.</p>
<div id="tableofcontents">
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<h2>Predefined directives</h2>
<p>The predefined directives are:</p>
<h3>#load "name"</h3>
<p>Loads an object file (ocaml cmo or cma file) in the core,
evaluating it. This is typically to be used in the ocaml toplevel
to add an syntax extension kit.</p>
<p>For example, in the toplevel, loading
the <a href="quot.html">quotation</a> expander
of <a href="ast_strict.html">ocaml syntax trees</a>:</p>
<pre>
# #load "q_MLast.cmo";
# value loc = Ploc.dummy;
value loc : Ploc.t = <abstr>
# <:expr< fun x -> x >>;
- : MLast.expr =
MLast.ExFun <abstr>
(Ploc.VaVal
[(MLast.PaLid <abstr> (Ploc.VaVal "x"), Ploc.VaVal None,
MLast.ExLid <abstr> (Ploc.VaVal "x"))])
</pre>
<p>In a source file, the '#load' directive is equivalent to put the
object file as camlp5 parameter among the 'load options':</p>
<pre>
$ cat myfile.ml
#load "pa_extend.cmo";
value g = Grammar.gcreate (Plexer.gmake ());
value e = Grammar.Entry.create g "e";
EXTEND e: [[ i = INT -> i ]]; END;
$ ocamlc -pp camlp5r -I +camlp5 -c myfile.ml
</pre>
<p>which is equivalent to, without using '#load':</p>
<pre>
$ cat myfile2.ml
value g = Grammar.gcreate (Plexer.gmake ());
value e = Grammar.Entry.create g "e";
EXTEND e: [[ i = INT -> i ]]; END;
</pre>
<p>and compiling it like this:</p>
<pre>
$ ocamlc -pp 'camlp5r pa_extend.cmo' -I +camlp5 -c myfile2.ml
</pre>
<h3>#directory "name"</h3>
<p>Adds a new directory in the camlp5 path searching for loaded files
(using the directive #load above). This is equivalent to the option
'-I' of the camlp5 command. See the camlp5 man page.</p>
<h3>#use "name"</h3>
<p>Loads a source file name. Useful in the ocaml toplevel to test a
source file.</p>
<h3>#option "option"</h3>
<p>Adds an option as if it were added in camlp5 command line (to be
used in a source file, not in the ocaml toplevel). Implemented
only on options without an extra parameter.</p>
<p>For example, the syntax
kit <a href="grammars.html">pa_extend.cmo</a> adds an option named
'-split_ext'. This can be viewed through the command:</p>
<pre>
camlp5r pa_extend.cmo -help
</pre>
<p>Thanks to the directive '#option', the following command in the
shell:</p>
<pre>
$ camlp5r pa_extend.cmo -split_ext file.ml
</pre>
<p>can be used only as:</p>
<pre>
$ camlp5r file.ml
</pre>
<p>providing the file starts with:</p>
<pre>
#load "pa_extend.cmo";
#option "-split_ext";
</pre>
<h2>User directives</h2>
<p>It is possible to add any extra directive. The syntax
kit <a href="pragma.html">pragma.cmo</a>, for example, adds a
directive named '#pragma'.</p>
<p>A user syntax kit can add its directives using the function
"add_directive" of the module <a href="pcaml.html">Pcaml</a>.</p>
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