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PRISM Manual | ThePRISMLanguage / FormulasAndLabels
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<p><a class='wikilink' href='Main.html'>The PRISM Language</a> /
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</p><h1>Formulas And Labels</h1>
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<p>PRISM models can include <em>formulas</em> which are used to avoid duplication of code.
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A formula comprises a name (an identifier) and an <a class='wikilink' href='Expressions.html'>expression</a>.
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The formula name can then be used as shorthand for the expression anywhere an expression might usually be accepted.
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A formula is defined as follows:
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<div class='vspace'></div>
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<div class='sourceblock ' id='sourceblock1'>
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<div class='sourceblocktext'><div class="prism"> <span class="prismkeyword">formula</span> <span class="prismident">num_tokens</span> = <span class="prismident">q1</span>+<span class="prismident">q2</span>+<span class="prismident">q3</span>+<span class="prismident">q</span>+<span class="prismident">q5</span>; <br/>
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</div></div>
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<div class='sourceblocklink'><a href='http://www.prismmodelchecker.org/manual/ThePRISMLanguage/FormulasAndLabels?action=sourceblock&num=1' type='text/plain'>[$[Get Code]]</a></div>
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</div>
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<p class='vspace'>It can then be used anywhere within that file, as for example in this command:
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</p>
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<div class='vspace'></div>
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<div class='sourceblock ' id='sourceblock2'>
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<div class='sourceblocktext'><div class="prism"> [] <span class="prismident">p1</span>=<span class="prismnum">2</span> & <span class="prismident">num_tokens</span>=<span class="prismnum">5</span> -> (<span class="prismident">p1</span>'=<span class="prismnum">4</span>); <br/>
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</div></div>
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<div class='sourceblocklink'><a href='http://www.prismmodelchecker.org/manual/ThePRISMLanguage/FormulasAndLabels?action=sourceblock&num=2' type='text/plain'>[$[Get Code]]</a></div>
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</div>
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<p class='vspace'>The effect is exactly as if the following had been typed:
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<div class='sourceblock ' id='sourceblock3'>
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<div class='sourceblocktext'><div class="prism"> [] <span class="prismident">p1</span>=<span class="prismnum">2</span> & (<span class="prismident">q1</span>+<span class="prismident">q2</span>+<span class="prismident">q3</span>+<span class="prismident">q</span>+<span class="prismident">q5</span>)=<span class="prismnum">5</span> -> (<span class="prismident">p1</span>'=<span class="prismnum">4</span>); <br/>
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</div></div>
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<div class='sourceblocklink'><a href='http://www.prismmodelchecker.org/manual/ThePRISMLanguage/FormulasAndLabels?action=sourceblock&num=3' type='text/plain'>[$[Get Code]]</a></div>
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</div>
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<p class='vspace'>Formulas defined in a model can also be used when specifying its properties.
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</p>
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<div class='vspace'></div><h3>Formulas and renaming</h3>
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<p>During parsing of the model, expansion of formulas is done before module renaming so, if a module which uses formulas is renamed to another module, it is the contents of the formula which will be renamed, not the formula itself.
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</p>
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<div class='vspace'></div><h3>Labels</h3>
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<p>PRISM models can also contain <em>labels</em>. These are are a way of identifying sets of states that are of particular interest. Labels can only be used when specifying <a class='wikilink' href='../PropertySpecification/Main.html'>properties</a> but, for convenience, can be defined in model files as well as property files.
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</p>
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<p class='vspace'>Labels differ from formulas in two other ways: firstly, they must be of Boolean type;
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secondly, they are written using quotation marks (<code>"..."</code>), as illustrated in the following example:
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</p>
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<div class='vspace'></div>
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<div class='sourceblock ' id='sourceblock4'>
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<div class='sourceblocktext'><div class="prism"><span class="prismkeyword">label</span> "<span class="prismident">safe</span>" = <span class="prismident">temp</span><=<span class="prismnum">100</span> | <span class="prismident">alarm</span>=<span class="prismkeyword">true</span>;<br/>
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<span class="prismkeyword">label</span> "<span class="prismident">fail</span>" = <span class="prismident">temp</span>><span class="prismnum">100</span> & <span class="prismident">alarm</span>=<span class="prismkeyword">false</span>;<br/>
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</div></div>
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<div class='sourceblocklink'><a href='http://www.prismmodelchecker.org/manual/ThePRISMLanguage/FormulasAndLabels?action=sourceblock&num=4' type='text/plain'>[$[Get Code]]</a></div>
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<h3><a class='wikilink' href='../Main/Main.html'>PRISM Manual</a></h3>
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<p><strong><a class='wikilink' href='Main.html'>The PRISM Language</a></strong>
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</p><ul><li><a class='wikilink' href='Main.html'>Introduction</a>
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</li><li><a class='wikilink' href='Example1.html'>Example 1</a>
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</li><li><a class='wikilink' href='ModelType.html'>Model Type</a>
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</li><li><a class='wikilink' href='ModulesAndVariables.html'>Modules And Variables</a>
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</li><li><a class='wikilink' href='Commands.html'>Commands</a>
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</li><li><a class='wikilink' href='ParallelComposition.html'>Parallel Composition</a>
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</li><li><a class='wikilink' href='LocalNondeterminism.html'>Local Nondeterminism</a>
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</li><li><a class='wikilink' href='CTMCs.html'>CTMCs</a>
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</li><li><a class='wikilink' href='Example2.html'>Example 2</a>
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</li><li><a class='wikilink' href='Constants.html'>Constants</a>
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</li><li><a class='wikilink' href='Expressions.html'>Expressions</a>
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</li><li><a class='wikilink' href='Synchronisation.html'>Synchronisation</a>
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</li><li><a class='wikilink' href='ModuleRenaming.html'>Module Renaming</a>
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</li><li><a class='wikilink' href='MultipleInitialStates.html'>Multiple Initial States</a>
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</li><li><a class='wikilink' href='GlobalVariables.html'>Global Variables</a>
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</li><li><a class='selflink' href='FormulasAndLabels.html'>Formulas And Labels</a>
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</li><li><a class='wikilink' href='PTAs.html'>PTAs</a>
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</li><li><a class='wikilink' href='CostsAndRewards.html'>Costs And Rewards</a>
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</li><li><a class='wikilink' href='ProcessAlgebraOperators.html'>Process Algebra Operators</a>
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</li><li><a class='wikilink' href='PRISMModelFiles.html'>PRISM Model Files</a>
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</li></ul><p>[ <a class='wikilink' href='AllOnOnePage.html'>View all</a> ]
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