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<title>Lexing</title>
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<h1>Module <a href="type_Lexing.html">Lexing</a></h1>
<pre><span id="MODULELexing"><span class="keyword">module</span> Lexing</span>: <code class="code"><span class="keyword">sig</span></code> <a href="Lexing.html">..</a> <code class="code"><span class="keyword">end</span></code></pre><div class="info module top">
<div class="info-desc">
<p>The run-time library for lexers generated by <code class="code">ocamllex</code>.</p>
</div>
</div>
<hr width="100%">
<h2 id="1_Positions">Positions</h2>
<pre><code><span id="TYPEposition"><span class="keyword">type</span> <code class="type"></code>position</span> = {</code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTposition.pos_fname">pos_fname</span> : <code class="type">string</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTposition.pos_lnum">pos_lnum</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTposition.pos_bol">pos_bol</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTposition.pos_cnum">pos_cnum</span> : <code class="type">int</code>;</code></td>
</tr></table>
<code>}</code>
<div class="info ">
<div class="info-desc">
<p>A value of type <code class="code">position</code> describes a point in a source file.
<code class="code">pos_fname</code> is the file name; <code class="code">pos_lnum</code> is the line number;
<code class="code">pos_bol</code> is the offset of the beginning of the line (number
of characters between the beginning of the lexbuf and the beginning
of the line); <code class="code">pos_cnum</code> is the offset of the position (number of
characters between the beginning of the lexbuf and the position).
The difference between <code class="code">pos_cnum</code> and <code class="code">pos_bol</code> is the character
offset within the line (i.e. the column number, assuming each
character is one column wide).</p>
<p>See the documentation of type <code class="code">lexbuf</code> for information about
how the lexing engine will manage positions.</p>
</div>
</div>
<pre><span id="VALdummy_pos"><span class="keyword">val</span> dummy_pos</span> : <code class="type"><a href="Lexing.html#TYPEposition">position</a></code></pre><div class="info ">
<div class="info-desc">
<p>A value of type <code class="code">position</code>, guaranteed to be different from any
valid position.</p>
</div>
</div>
<h2 id="1_Lexerbuffers">Lexer buffers</h2>
<pre><code><span id="TYPElexbuf"><span class="keyword">type</span> <code class="type"></code>lexbuf</span> = {</code></pre><table class="typetable">
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span id="TYPEELTlexbuf.refill_buff">refill_buff</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> unit</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_buffer">lex_buffer</span> : <code class="type">bytes</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_buffer_len">lex_buffer_len</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_abs_pos">lex_abs_pos</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_start_pos">lex_start_pos</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_curr_pos">lex_curr_pos</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_last_pos">lex_last_pos</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_last_action">lex_last_action</span> : <code class="type">int</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_eof_reached">lex_eof_reached</span> : <code class="type">bool</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_mem">lex_mem</span> : <code class="type">int array</code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_start_p">lex_start_p</span> : <code class="type"><a href="Lexing.html#TYPEposition">position</a></code>;</code></td>
</tr>
<tr>
<td align="left" valign="top" >
<code> </code></td>
<td align="left" valign="top" >
<code><span class="keyword">mutable </span><span id="TYPEELTlexbuf.lex_curr_p">lex_curr_p</span> : <code class="type"><a href="Lexing.html#TYPEposition">position</a></code>;</code></td>
</tr></table>
<code>}</code>
<div class="info ">
<div class="info-desc">
<p>The type of lexer buffers. A lexer buffer is the argument passed
to the scanning functions defined by the generated scanners.
The lexer buffer holds the current state of the scanner, plus
a function to refill the buffer from the input.</p>
<p>Lexers can optionally maintain the <code class="code">lex_curr_p</code> and <code class="code">lex_start_p</code>
position fields. This "position tracking" mode is the default, and
it corresponds to passing <code class="code">~with_position:<span class="keyword">true</span></code> to functions that
create lexer buffers. In this mode, the lexing engine and lexer
actions are co-responsible for properly updating the position
fields, as described in the next paragraph. When the mode is
explicitly disabled (with <code class="code">~with_position:<span class="keyword">false</span></code>), the lexing
engine will not touch the position fields and the lexer actions
should be careful not to do it either; the <code class="code">lex_curr_p</code> and
<code class="code">lex_start_p</code> field will then always hold the <code class="code">dummy_pos</code> invalid
position. Not tracking positions avoids allocations and memory
writes and can significantly improve the performance of the lexer
in contexts where <code class="code">lex_start_p</code> and <code class="code">lex_curr_p</code> are not needed.</p>
<p>Position tracking mode works as follows. At each token, the lexing
engine will copy <code class="code">lex_curr_p</code> to <code class="code">lex_start_p</code>, then change the
<code class="code">pos_cnum</code> field of <code class="code">lex_curr_p</code> by updating it with the number of
characters read since the start of the <code class="code">lexbuf</code>. The other fields
are left unchanged by the lexing engine. In order to keep them
accurate, they must be initialised before the first use of the
lexbuf, and updated by the relevant lexer actions (i.e. at each end
of line -- see also <code class="code">new_line</code>).</p>
</div>
</div>
<pre><span id="VALfrom_channel"><span class="keyword">val</span> from_channel</span> : <code class="type">?with_positions:bool -> <a href="Stdlib.html#TYPEin_channel">in_channel</a> -> <a href="Lexing.html#TYPElexbuf">lexbuf</a></code></pre><div class="info ">
<div class="info-desc">
<p>Create a lexer buffer on the given input channel.
<code class="code"><span class="constructor">Lexing</span>.from_channel inchan</code> returns a lexer buffer which reads
from the input channel <code class="code">inchan</code>, at the current reading position.</p>
</div>
</div>
<pre><span id="VALfrom_string"><span class="keyword">val</span> from_string</span> : <code class="type">?with_positions:bool -> string -> <a href="Lexing.html#TYPElexbuf">lexbuf</a></code></pre><div class="info ">
<div class="info-desc">
<p>Create a lexer buffer which reads from
the given string. Reading starts from the first character in
the string. An end-of-input condition is generated when the
end of the string is reached.</p>
</div>
</div>
<pre><span id="VALfrom_function"><span class="keyword">val</span> from_function</span> : <code class="type">?with_positions:bool -> (bytes -> int -> int) -> <a href="Lexing.html#TYPElexbuf">lexbuf</a></code></pre><div class="info ">
<div class="info-desc">
<p>Create a lexer buffer with the given function as its reading method.
When the scanner needs more characters, it will call the given
function, giving it a byte sequence <code class="code">s</code> and a byte
count <code class="code">n</code>. The function should put <code class="code">n</code> bytes or fewer in <code class="code">s</code>,
starting at index 0, and return the number of bytes
provided. A return value of 0 means end of input.</p>
</div>
</div>
<pre><span id="VALset_position"><span class="keyword">val</span> set_position</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> <a href="Lexing.html#TYPEposition">position</a> -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Set the initial tracked input position for <code class="code">lexbuf</code> to a custom value.
Ignores <code class="code">pos_fname</code>. See <a href="Lexing.html#VALset_filename"><code class="code"><span class="constructor">Lexing</span>.set_filename</code></a> for changing this field.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 4.11</li>
</ul>
</div>
<pre><span id="VALset_filename"><span class="keyword">val</span> set_filename</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> string -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Set filename in the initial tracked position to <code class="code">file</code> in
<code class="code">lexbuf</code>.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 4.11</li>
</ul>
</div>
<pre><span id="VALwith_positions"><span class="keyword">val</span> with_positions</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> bool</code></pre><div class="info ">
<div class="info-desc">
<p>Tell whether the lexer buffer keeps track of position fields
<code class="code">lex_curr_p</code> / <code class="code">lex_start_p</code>, as determined by the corresponding
optional argument for functions that create lexer buffers
(whose default value is <code class="code"><span class="keyword">true</span></code>).</p>
<p>When <code class="code">with_positions</code> is <code class="code"><span class="keyword">false</span></code>, lexer actions should not
modify position fields. Doing it nevertheless could
re-enable the <code class="code">with_position</code> mode and degrade performances.</p>
</div>
</div>
<h2 id="1_Functionsforlexersemanticactions">Functions for lexer semantic actions</h2><p>The following functions can be called from the semantic actions
of lexer definitions (the ML code enclosed in braces that
computes the value returned by lexing functions). They give
access to the character string matched by the regular expression
associated with the semantic action. These functions must be
applied to the argument <code class="code">lexbuf</code>, which, in the code generated by
<code class="code">ocamllex</code>, is bound to the lexer buffer passed to the parsing
function.</p>
<pre><span id="VALlexeme"><span class="keyword">val</span> lexeme</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> string</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code"><span class="constructor">Lexing</span>.lexeme lexbuf</code> returns the string matched by
the regular expression.</p>
</div>
</div>
<pre><span id="VALlexeme_char"><span class="keyword">val</span> lexeme_char</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> int -> char</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code"><span class="constructor">Lexing</span>.lexeme_char lexbuf i</code> returns character number <code class="code">i</code> in
the matched string.</p>
</div>
</div>
<pre><span id="VALlexeme_start"><span class="keyword">val</span> lexeme_start</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> int</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code"><span class="constructor">Lexing</span>.lexeme_start lexbuf</code> returns the offset in the
input stream of the first character of the matched string.
The first character of the stream has offset 0.</p>
</div>
</div>
<pre><span id="VALlexeme_end"><span class="keyword">val</span> lexeme_end</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> int</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code"><span class="constructor">Lexing</span>.lexeme_end lexbuf</code> returns the offset in the input stream
of the character following the last character of the matched
string. The first character of the stream has offset 0.</p>
</div>
</div>
<pre><span id="VALlexeme_start_p"><span class="keyword">val</span> lexeme_start_p</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> <a href="Lexing.html#TYPEposition">position</a></code></pre><div class="info ">
<div class="info-desc">
<p>Like <code class="code">lexeme_start</code>, but return a complete <code class="code">position</code> instead
of an offset. When position tracking is disabled, the function
returns <code class="code">dummy_pos</code>.</p>
</div>
</div>
<pre><span id="VALlexeme_end_p"><span class="keyword">val</span> lexeme_end_p</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> <a href="Lexing.html#TYPEposition">position</a></code></pre><div class="info ">
<div class="info-desc">
<p>Like <code class="code">lexeme_end</code>, but return a complete <code class="code">position</code> instead
of an offset. When position tracking is disabled, the function
returns <code class="code">dummy_pos</code>.</p>
</div>
</div>
<pre><span id="VALnew_line"><span class="keyword">val</span> new_line</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Update the <code class="code">lex_curr_p</code> field of the lexbuf to reflect the start
of a new line. You can call this function in the semantic action
of the rule that matches the end-of-line character. The function
does nothing when position tracking is disabled.</p>
</div>
<ul class="info-attributes">
<li><b>Since</b> 3.11.0</li>
</ul>
</div>
<h2 id="1_Miscellaneousfunctions">Miscellaneous functions</h2>
<pre><span id="VALflush_input"><span class="keyword">val</span> flush_input</span> : <code class="type"><a href="Lexing.html#TYPElexbuf">lexbuf</a> -> unit</code></pre><div class="info ">
<div class="info-desc">
<p>Discard the contents of the buffer and reset the current
position to 0. The next use of the lexbuf will trigger a
refill.</p>
</div>
</div>
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