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5daee73ce4
Hydra passes the full revision in to the input, which we pass through. If we don't get this ,we try to get it from other sources, or default to master which should have the definition in a close-ish location. All published docs should have theURL resolve properly, only local hackers will have the link break.
118 lines
3 KiB
XML
118 lines
3 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xml:id="sec-functions-library-asserts">
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<title>Assert functions</title>
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<section xml:id="function-library-lib.asserts.assertMsg">
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<title><function>lib.asserts.assertMsg</function></title>
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<subtitle><literal>assertMsg :: Bool -> String -> Bool</literal>
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</subtitle>
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<xi:include href="./locations.xml" xpointer="lib.asserts.assertMsg" />
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<para>
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Print a trace message if <literal>pred</literal> is false.
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</para>
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<para>
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Intended to be used to augment asserts with helpful error messages.
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</para>
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<variablelist>
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<varlistentry>
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<term>
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<varname>pred</varname>
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</term>
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<listitem>
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<para>
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Condition under which the <varname>msg</varname> should
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<emphasis>not</emphasis> be printed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>msg</varname>
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</term>
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<listitem>
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<para>
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Message to print.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<example xml:id="function-library-lib.asserts.assertMsg-example-false">
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<title>Printing when the predicate is false</title>
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<programlisting><![CDATA[
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assert lib.asserts.assertMsg ("foo" == "bar") "foo is not bar, silly"
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stderr> trace: foo is not bar, silly
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stderr> assert failed
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]]></programlisting>
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</example>
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</section>
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<section xml:id="function-library-lib.asserts.assertOneOf">
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<title><function>lib.asserts.assertOneOf</function></title>
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<subtitle><literal>assertOneOf :: String -> String ->
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StringList -> Bool</literal>
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</subtitle>
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<xi:include href="./locations.xml" xpointer="lib.asserts.assertOneOf" />
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<para>
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Specialized <function>asserts.assertMsg</function> for checking if
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<varname>val</varname> is one of the elements of <varname>xs</varname>.
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Useful for checking enums.
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</para>
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<variablelist>
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<varlistentry>
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<term>
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<varname>name</varname>
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</term>
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<listitem>
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<para>
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The name of the variable the user entered <varname>val</varname> into,
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for inclusion in the error message.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>val</varname>
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</term>
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<listitem>
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<para>
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The value of what the user provided, to be compared against the values in
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<varname>xs</varname>.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<varname>xs</varname>
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</term>
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<listitem>
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<para>
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The list of valid values.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<example xml:id="function-library-lib.asserts.assertOneOf-example">
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<title>Ensuring a user provided a possible value</title>
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<programlisting><![CDATA[
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let sslLibrary = "bearssl";
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in lib.asserts.assertOneOf "sslLibrary" sslLibrary [ "openssl" "bearssl" ];
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=> false
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stderr> trace: sslLibrary must be one of "openssl", "libressl", but is: "bearssl"
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]]></programlisting>
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</example>
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</section>
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</section>
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