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<title>Ocamlnet 2 Reference Manual : Netulex_tut</title> </head> <body> <div class="navbar"><a href="Netsendmail_tut.html">Previous</a> <a href="index.html">Up</a> <a href="Neturl_tut.html">Next</a> </div> <center><h1>Netulex_tut</h1></center> <br> <br> <a name="tutorial"></a> <h1>Netulex Tutorial</h1> <p> Of course, you need Alain Frisch's <code class="code">ulex</code> utility first. It installs itself under the name <code class="code">ulex</code> as findlib library. <p> Next, write your lexer, e.g. (line numbers in brackets): <p> <pre><code class="code">[1] open Netulex [2] let digits = lexer [3] | ['0'-'9']+ -> `Number(int_of_string(Ulexing.utf8_lexeme lexbuf)) [4] | 8364 -> `Euro_sign (* Code point #8364 in Unicode *) </code></pre> <p> This is a very trivial example. The lexer accepts sequences of digits, and returns them as `Number tokens. Furthermore, the euro sign is recognized and returned as `Euro_sign. Note that in the first case <a href="Netulex.Ulexing.html#VALutf8_lexeme"><code class="code">Netulex.Ulexing.utf8_lexeme</code></a> is called to retrieve the current lexeme as UTF-8 string. (Well, digits are a bad example, as they are only ASCII, and UTF-8 is not really needed. Imagine you want to extend the scanner to other number systems represented in the Unicode character set.) <p> Line 1 is quite important. If you don't open <code class="code">Netulex</code>, the generated <code class="code">ulex</code> code will use the version of the <code class="code">Ulexing</code> module coming with <code class="code">ulex</code>, and not this one. <p> Call the lexer as follows (line numbers in brackets): <pre><code class="code">[5] let sample = "42543\226\130\172";; [6] let ulb = Netulex.ULB.from_string `Enc_utf8 sample;; [7] let lexbuf = Netulex.Ulexing.from_ulb_lexbuf ulb;; [8] let first_token = digits lexbuf;; </code></pre> <p> Now, <code class="code">first_token</code> is <code class="code">`Number 42543</code>. After <p> <pre><code class="code">[9] let second_token = digits lexbuf;; </code></pre> <p> this variable is set to <code class="code">`Euro_sign</code>, because the three-byte sequence "\226\130\172" represents the euro sign in UTF-8. <p> In line 6, the encoding <code class="code">`Enc_utf8</code> selects that <code class="code">sample</code> is an UTF-8 string. You can pass here any encoding the <a href="Netconversion.html"><code class="code">Netconversion</code></a> module understands. <p> If you would like to scan from another source, just change line 6, e.g. <p> <pre><code class="code">[6'] let ulb = Netulex.ULB.from_in_obj_channel ch </code></pre> <p> where <code class="code">ch</code> is any input channel the <a href="Netchannels.html"><code class="code">Netchannels</code></a> module supports. For example, to read from a file: <p> <pre><code class="code">let ch = new Netchannels.input_channel (open_in "filename") </code></pre> <p> You should compile the examples with <p> <pre><code class="code">ocamlfind ... -package ulex,netstring -syntax camlp4o ... </code></pre> <p> For the syntax of the lexer rules, see the documentation coming with <code class="code">ulex</code>. <p> <br> </body></html>
