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- <!DOCTYPE html><html><head><meta http-equiv="content-type" content="text/html;charset=utf-8"><title>Interpreter.java</title><link href="../../../../css/bootstrap.min.css" rel="stylesheet" type="text/css"/><link href="../../../../css/bootstrap-responsive.min.css" rel="stylesheet" type="text/css"/><link href="../../../../css/atlassian-docco.css" rel="stylesheet" type="text/css"/><link rel="stylesheet" class="codebrush light" title="IDEA" href="http://yandex.st/highlightjs/6.2/styles/idea.min.css"/><link rel="alternate stylesheet" class="codebrush light" title="Google Code" href="http://yandex.st/highlightjs/6.2/styles/googlecode.min.css"/><link rel="alternate stylesheet" class="codebrush light" title="GitHub" href="http://yandex.st/highlightjs/6.2/styles/github.min.css"/><link rel="alternate stylesheet" class="codebrush light" title="Visual Studio" href="http://yandex.st/highlightjs/6.2/styles/vs.min.css"/><link rel="alternate stylesheet" class="codebrush light" title="Magula" 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href="../../../../src/main/java/expression/Expression.java.html">Expression.java</a></li><li><a href="../../../../src/main/java/expression/Identifier.java.html">Identifier.java</a></li><li><a href="../../../../src/main/java/expression/Int.java.html">Int.java</a></li><li><a href="../../../../src/main/java/expression/Subtraction.java.html">Subtraction.java</a></li><li class="nav-header">Interpreter</li><li><a href="../../../../src/main/java/interpreter/Evaluator.java.html">Evaluator.java</a></li><li class="active"><a href="../../../../src/main/java/interpreter/Interpreter.java.html">Interpreter.java</a></li><li><a href="../../../../src/main/java/interpreter/InterpreterException.java.html">InterpreterException.java</a></li><li><a href="../../../../src/main/java/interpreter/Visitor.java.html">Visitor.java</a></li><li class="nav-header">Parser</li><li><a href="../../../../src/main/java/parser/Parser.java.html">Parser.java</a></li><li><a href="../../../../src/main/java/parser/SyntaxException.java.html">SyntaxException.java</a></li><li class="nav-header">Printer</li><li><a href="../../../../src/main/java/printer/ExpressionPrinter.java.html">ExpressionPrinter.java</a></li><li><a href="../../../../src/main/java/printer/ProgramPrinter.java.html">ProgramPrinter.java</a></li><li class="nav-header">Program</li><li><a href="../../../../src/main/java/program/Assignment.java.html">Assignment.java</a></li><li><a href="../../../../src/main/java/program/Composition.java.html">Composition.java</a></li><li><a href="../../../../src/main/java/program/Conditional.java.html">Conditional.java</a></li><li><a href="../../../../src/main/java/program/Loop.java.html">Loop.java</a></li><li><a href="../../../../src/main/java/program/Program.java.html">Program.java</a></li></ul></li><li class="dropdown"><a href="#" class="dropdown-toggle" data-toggle="dropdown">Theme <b class="caret"></b></a><ul id="themeDropdown" class="dropdown-menu"></ul></li><li class="dropdown"><a href="#" class="dropdown-toggle" data-toggle="dropdown">Layout <b class="caret"></b></a><ul class="dropdown-menu"><li class="active"><a href="#">Horizontal</a></li><li><a href="../../../../../vertical/src/main/java/interpreter/Interpreter.java.html">Vertical</a></li></ul></li></ul></div><!--/.nav-collapse --></div></div></div><div class="container-fluid docco-container"><div class="row-fluid"><div class="span12"><h1>Interpreter</h1><p>The interpreter consists of the <code>Interpreter</code> defined in this file that can run a <code>Program</code> and the <code>Evaluator</code> that can evaluate an <code>Expression</code>.</p><p>The interpreter implements the semantics defined by the function <code>sem: Prog * V -> V</code>, where <code>V = Id -> Z</code> is the set of all variable valuations to the set <code>Z</code> set of integers. <code>sem</code> is inductively defined as follows:</p>
- <pre><code>sem(x ":=" e, v) = v.update(x, eval(e, v))
- sem(c1 ";" c2) = sem(c2, sem(c1, v))
- sem("if" "(" e ")" "then" "{" c1 "}" else "{" c2 "}") =
- sem(c1, v) if eval(e, v) != 0
- sem(c2, v) else
- sem("while" "(" e ")" "{" c "}", v) =
- sem(c ";" "while" "(" e ")" "{" c "}", v) if eval(e, v) != 0
- v else
- </code></pre><p>with</p>
- <ul>
- <li>a variable valuation <code>v</code>,</li>
- <li>an expression <code>e</code>,</li>
- <li>an identifier <code>x</code> and</li>
- <li>programs <code>c</code>, <code>c1</code>, <code>c2</code>.</li>
- </ul><p>The evaluation function <code>eval</code> is described at the <a href="../../../../src/main/java/interpreter/Evaluator.java.html">Evaluator</a>.</p></div></div><div id="section-0" class="row-fluid docco-section"><div class="span6 doc"><span class="label label-info"><a style="color:white" href="#section-0">0</a></span><div class="doctext hidden-doc"></div></div><div class="span6 code"><div class="hidden-code-line">------------------<a href="javascript:void(0)" class="hidden-code-toggle" index="0">Show Header Code (<span class="linecount"></span> lines)</a>------------------</div><pre class="hidden-code"><code class="java">package interpreter;
-
- import program.*;
-
- import java.util.HashMap;
- import java.util.Map;</code></pre></div></div><div id="section-1" class="row-fluid docco-section"><div class="span6 doc"><span class="label label-info"><a style="color:white" href="#section-1">1</a></span><div class="doctext"><p>The <code>Interpreter</code> implements the semantic function defined above with the help of the <a href="../../../../src/main/java/interpreter/Visitor.java.html">Visitor</a>. The <code>Interpreter</code> runs the given <code>Program</code> in the constructor and can be used as follows on a given <code>program</code> of type <code>Program</code>.</p>
- <pre><code>Interpreter interpreter = new Interpreter(program);
- System.out.println(interpreter.getValuation());
- </code></pre><p>The semantic function <code>sem</code> passes along the variable valuation <code>v</code>. In the <code>Interpreter</code> the valuation is realized as global variable <code>valuation</code>. Because of the in-order execution this global variable always represents the state of the <code>v</code> passed to the semantic function <code>sem</code>. </p></div></div><div class="span6 code"><pre><code class="java">public class Interpreter extends Visitor {
- private final Map<String, Integer> valuation = new HashMap<String, Integer>();
-
- public Map<String, Integer> getValuation() {
- Map<String, Integer> result = new HashMap<String, Integer>();
- result.putAll(valuation);
- return result;
- }
-
- public Interpreter(Program program) {
- visit(program);
- }</code></pre></div></div><div id="section-2" class="row-fluid docco-section"><div class="span6 doc"><span class="label label-info"><a style="color:white" href="#section-2">2</a></span><div class="doctext"><pre><code>sem(x ":=" e, v) = v.update(x, eval(e, v))
- </code></pre></div></div><div class="span6 code"><pre><code class="java"> public void visitAssignment(Assignment assignment) {
- Evaluator evaluator = new Evaluator(assignment.expression, valuation);
- valuation.put(assignment.identifier.name, evaluator.getValue());
- }</code></pre></div></div><div id="section-3" class="row-fluid docco-section"><div class="span6 doc"><span class="label label-info"><a style="color:white" href="#section-3">3</a></span><div class="doctext"><pre><code>sem(c1 ";" c2) = sem(c2, sem(c1, v))
- </code></pre></div></div><div class="span6 code"><pre><code class="java"> public void visitComposition(Composition composition) {
- visit(composition.first);
- visit(composition.second);
- }</code></pre></div></div><div id="section-4" class="row-fluid docco-section"><div class="span6 doc"><span class="label label-info"><a style="color:white" href="#section-4">4</a></span><div class="doctext"><pre><code>sem("if" "(" e ")" "then" "{" c1 "}" else "{" c2 "}") =
- sem(c1, v) if eval(e, v) != 0
- sem(c2, v) else
- </code></pre></div></div><div class="span6 code"><pre><code class="java"> public void visitConditional(Conditional conditional) {
- Evaluator evaluator = new Evaluator(conditional.condition, valuation);
- if (evaluator.getValue() != 0) {
- visit(conditional.thenCase);
- } else {
- visit(conditional.elseCase);
- }
- }</code></pre></div></div><div id="section-5" class="row-fluid docco-section"><div class="span6 doc"><span class="label label-info"><a style="color:white" href="#section-5">5</a></span><div class="doctext"><pre><code>sem("while" "(" e ")" "{" c "}", v) =
- sem(c ";" "while" "(" e ")" "{" c "}", v) if eval(e, v) != 0
- v else
- </code></pre></div></div><div class="span6 code"><pre><code class="java"> public void visitLoop(Loop loop) {
- Evaluator evaluator = new Evaluator(loop.condition, valuation);
- if (evaluator.getValue() != 0) {
- visit(new Composition(loop.program, loop));
- }
- }
- }</code></pre></div></div></div><div id="grabber"></div></body></html>
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