From a6447679032d997d861f4f397ae3e21806726739 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Tue, 29 Sep 2015 20:19:28 +0100
Subject: Move Evaluator to its own class

---
 .../zwobble/couscous/interpreter/Evaluator.java    | 41 ++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 src/main/java/org/zwobble/couscous/interpreter/Evaluator.java

(limited to 'src/main/java/org/zwobble/couscous/interpreter/Evaluator.java')

diff --git a/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
new file mode 100644
index 0000000..033bfb8
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/Evaluator.java
@@ -0,0 +1,41 @@
+package org.zwobble.couscous.interpreter;
+
+import java.util.Map;
+
+import org.zwobble.couscous.ast.Assignment;
+import org.zwobble.couscous.ast.ExpressionNode;
+import org.zwobble.couscous.ast.LiteralNode;
+import org.zwobble.couscous.ast.VariableReferenceNode;
+import org.zwobble.couscous.ast.visitors.ExpressionNodeVisitor;
+import org.zwobble.couscous.values.InterpreterValue;
+
+import lombok.val;
+
+public class Evaluator implements ExpressionNodeVisitor<InterpreterValue> {
+    private final Map<Integer, InterpreterValue> stackFrame;
+
+    public Evaluator(Map<Integer, InterpreterValue> stackFrame) {
+        this.stackFrame = stackFrame;
+    }
+    
+    public InterpreterValue eval(ExpressionNode expression) {
+        return expression.accept(this);
+    }
+
+    @Override
+    public InterpreterValue visit(LiteralNode literal) {
+        return literal.getValue();
+    }
+
+    @Override
+    public InterpreterValue visit(VariableReferenceNode variableReference) {
+        return stackFrame.get(variableReference.getReferentId());
+    }
+
+    @Override
+    public InterpreterValue visit(Assignment assignment) {
+        val value = eval(assignment.getValue());
+        stackFrame.put(assignment.getTarget().getReferentId(), value);
+        return value;
+    }
+}
-- 
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