tame/core/assert.xml

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<?xml version="1.0"?>
<!--
Copyright (C) 2015, 2018 R-T Specialty, LLC.
This file is part of tame-core.
tame-core is free software: you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
-->
<package xmlns="http://www.lovullo.com/rater"
xmlns:t="http://www.lovullo.com/rater/apply-template"
core="true"
desc="Assertions">
<import package="base" />
<import package="vector/cmatch" export="true" />
This package is young;
the intent is to provide basic assertions to ensure data
integrity.
\emph{N.B. The behavior of this package changed in version 1.0.0---%
\ref{_assert_} now properly fails on non-match,
not match.}
The \ref{_assert_} template generates a~generic assertion using the
provided predicates.
If the predicates provided to the assertion fail (yields $\bot$),
the system immediately terminates.\footnote{
Beacuse the system stops processing once a terminating classification
yields~$\top$,
only one assertion will ever match,
even if others would match if execution were to continue.}
\tt{@class@} may optionally be used to predicate the asseriton itself---%
the assertion will be performed only on respective class matches.
\ref{_assert_} implements assertions by genearting two classifications---%
one to perform the actual assertion,
and a terminating classification to ensure that the assertion
yields~$\top$.
<template name="_assert_"
desc="Terminate on predicate failure">
<param name="@values@" desc="Predicates" />
<param name="@as@" desc="Generated classification name">
<text unique="true">-assert-</text>
</param>
<param name="@failure@" desc="Failure description">
<text>Assertion</text>
</param>
<param name="@class@" desc="Only perform assertion for respective class
matches (optional)" />
<param name="@neg_as@"
desc="Generated name for classification to be negated">
<text unique="true">-nassert-</text>
</param>
<param name="@neg_yields@"
desc="Generated yield for classification to be negated">
<text unique="true">_nassert</text>
</param>
<!-- The actual assertion will be performed by one classification... -->
<classify as="@neg_as@" yields="@neg_yields@"
desc="{@failure@} (assertion result)">
<any>
<!-- if class is provided and does not match, then the assertion
succeeds automatically -->
<if name="@class@">
<t:match-class name="@class@" value="FALSE" />
</if>
<all>
<param-copy name="@values@" />
</all>
</any>
</classify>
<!-- ...which is in turn negated for the terminating
classification. The reason for this is that terminating
classifications terminate on _match_. -->
<classify as="@as@" desc="@failure@" terminate="true">
<match on="@neg_yields@" value="FALSE" />
</classify>
</template>
</package>