| <html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>5.5.1. ASM Function Definition</title><link href="style.css" rel="stylesheet" type="text/css"><meta content="DocBook XSL Stylesheets V1.72.0" name="generator"><link rel="start" href="index.html" title="The VIATRA2 Model Transformation Framework"><link rel="up" href="sec_ASMFunctions.html" title="5.5. ASM Functions"><link rel="prev" href="sec_ASMFunctions.html" title="5.5. ASM Functions"><link rel="next" href="def_InitialValue.html" title="5.5.2. Initial Value"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table summary="Navigation header" width="100%"><tr><th align="center" colspan="3">5.5.1. ASM Function Definition</th></tr><tr><td align="left" width="20%"><a accesskey="p" href="sec_ASMFunctions.html">Prev</a> </td><th align="center" width="60%">5.5. ASM Functions</th><td align="right" width="20%"> <a accesskey="n" href="def_InitialValue.html">Next</a></td></tr></table><hr></div><div class="sect3" lang="en"><div class="titlepage"><div><div><h4 class="title"><a name="def_AsmFunctionDef"></a>5.5.1. ASM Function Definition</h4></div></div></div><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip: Description"><tr><td valign="top" align="center" rowspan="2" width="25"><img alt="[Tip]" src="images/tip.png"></td><th align="left"><a name="def_AsmFunctionDef_Description"></a>Description</th></tr><tr><td valign="top" align="left"><p> | |
| In terms of structured programming languages, an <span class="strong"><strong>ASM function definition</strong></span> | |
| <a name="N12B96" class="indexterm"></a> | |
| is an associative array (dictionary, map, etc.), which stores | |
| <span class="emphasis"><em>data values</em></span> at <a href="def_AsmFunctionLocation.html" title="5.5.3. ASM Function Location">locations</a> (slots) defined by its | |
| <span class="emphasis"><em>index elements</em></span>. However, a main difference is that these arrays are | |
| very dynamic in the sense that they may store an arbitrarily large number of | |
| elements, and the size of the array can be increased at any time during | |
| execution in order to store a new element at a specific location (index). | |
| </p></td></tr></table></div><div class="important" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Important: Syntax"><tr><td valign="top" align="center" rowspan="2" width="25"><img alt="[Important]" src="images/important.png"></td><th align="left"><a name="def_AsmFunctionDef_Syntax"></a>Syntax</th></tr><tr><td valign="top" align="left"><pre class="programlisting"> | |
| AsmFunctionDefAST ::= <a href="def_Annotation.html" title="1.2.2. Annotation">OptAnnotationsAST</a> <span class="token">asmfunction</span> <a href="def_ModelElementName.html" title="5.7.1. Model Element Name">TypeNameAST</a> <span class="token">/</span> ArityAST <a href="def_InitialValue.html" title="5.5.2. Initial Value">InitialValuesOptAST</a> | |
| ArityAST ::= DecimalIntegerLiteral | |
| </pre><p> | |
| An <code class="computeroutput">ASM function</code> is identified by its | |
| <a href="def_ModelElementName.html" title="5.7.1. Model Element Name">name</a> and its <span class="strong"><strong>arity</strong></span>, | |
| <a name="N12BCE" class="indexterm"></a> | |
| <a name="N12BD5" class="indexterm"></a> | |
| which is the number of dimensions of the corresponding associative array. | |
| In addition, we may optionally provided initial definitions of some slots storing some | |
| values at certain locations (<a href="def_InitialValue.html" title="5.5.2. Initial Value">initial value</a>). | |
| Unused locations of arrays are implicitly storing the <span class="emphasis"><em>undef</em></span> value. | |
| </p><p> | |
| An ASM function have to be declared at the global scope (that is, at machine | |
| scope, outside any rules) prior to its first use. | |
| </p></td></tr></table></div><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note: Semantics"><tr><td valign="top" align="center" rowspan="2" width="25"><img alt="[Note]" src="images/note.png"></td><th align="left"><a name="def_AsmFunctionDef_Semantics"></a>Semantics</th></tr><tr><td valign="top" align="left"><p> | |
| Mathematically, an ASM function is a partial mapping from its index domain | |
| (called location or slot) to its value domain. | |
| </p><p> | |
| While ASM variables have a local scope in the sense that a variable becomes | |
| non-accessible as soon as the execution leaves the rule (or the block) of its | |
| scope, <span class="emphasis"><em>ASM functions</em></span>have a global visibility, thus they are | |
| accessible from anywhere <span class="emphasis"><em>during the entire run of an ASM machine</em></span>. However, | |
| the location-value assignments are not persistent, i.e. these are not | |
| preserved between different runs of ASM machines (as it is the case in case | |
| of model elements in the VPM model space). | |
| </p><p> | |
| Since ASM functions defined in other machines can also be invoked, the | |
| interpreter provides lazy initialization for all ASM functions: these are | |
| <span class="emphasis"><em>initialized on-demand</em></span>, i.e. just before their first use. | |
| </p></td></tr></table></div><div class="highlights"><a name="def_AsmFunctionDef_DefinedIn"></a><p><b>Defined In: </b> | |
| <a href="def_Machine.html" title="1.2.1. GTASM Machine Definition">GTASM Machine</a> | |
| </p></div><div class="highlights"><a name="def_AsmFunctionDef_SeeAlso"></a><p><b>See Also: </b> | |
| <a href="def_AsmFunctionLocation.html" title="5.5.3. ASM Function Location">ASM function location</a>, | |
| <a href="def_UpdateRule.html" title="4.2.5. Update Rule">update rule</a> | |
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