36 lines
1.8 KiB
XML
36 lines
1.8 KiB
XML
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<chapter id="ljp.bml.core">
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<chapterinfo>
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<title>Core <abbrev>BML</abbrev> blocks</title>
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</chapterinfo>
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<title>Core <abbrev>BML</abbrev> blocks</title>
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<para>
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Core blocks are predefined blocks that are named with a leading underscore.
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Most core blocks have a higher purpose than simple template use:
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</para>
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<variablelist>
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<varlistentry>
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<term><literal role="core.bml.block">_code</literal></term>
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<listitem><para>
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<literal><?_code _code?></literal> blocks are perhaps the most useful feature of
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<abbrev>BML</abbrev> outside of the ability to have global site templates.
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These blocks allow template authors to embed pieces of executable Perl code
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within the bml page that get executed on the server.
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</para><para>
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</para><para>
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The code you write gets executed in its own package (namespace) called
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<computeroutput>BMLCodeBlock::</computeroutput>.
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Any variables you declare in one code block on a page without using
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<literal>my</literal> are carried on to the next <literal>_code</literal> block.
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</para><para>
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Because the BML parser must evaluate everything on the page before sending the
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<abbrev>HTTP</abbrev> headers, make sure you don't print anything.
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Any output printed to <literal>STDOUT</literal> will just be interpreted as
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<abbrev>HTTP</abbrev> headers. How the <literal>_code</literal> blocks work is
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that you need to return a value at the end.
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Whatever value your code fragment returns is what the block evaluates to.
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Usually what you end up doing is building a string, concatenating things to it
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over and over, and then returning it at the end.
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</para></listitem>
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</varlistentry>
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</variablelist>
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</chapter>
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