1 files changed, 110 insertions, 0 deletions
diff --git a/src/main/java/org/zwobble/couscous/interpreter/Interpreter.java b/src/main/java/org/zwobble/couscous/interpreter/Interpreter.java
new file mode 100644
index 0000000..49c651b
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/Interpreter.java
@@ -0,0 +1,110 @@
+package org.zwobble.couscous.interpreter;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.IntStream;
+
+import org.zwobble.couscous.Project;
+import org.zwobble.couscous.ast.Assignment;
+import org.zwobble.couscous.ast.ExpressionNode;
+import org.zwobble.couscous.ast.ExpressionStatementNode;
+import org.zwobble.couscous.ast.LiteralNode;
+import org.zwobble.couscous.ast.MethodNode;
+import org.zwobble.couscous.ast.ReturnNode;
+import org.zwobble.couscous.ast.VariableReferenceNode;
+import org.zwobble.couscous.ast.visitors.ExpressionNodeVisitor;
+import org.zwobble.couscous.ast.visitors.StatementNodeVisitor;
+import org.zwobble.couscous.values.InterpreterValue;
+
+import static com.google.common.collect.Iterables.find;
+import static java.util.stream.Collectors.toMap;
+import static org.zwobble.couscous.values.UnitValue.UNIT;
+
+import lombok.val;
+
+public class Interpreter {
+    private Project project;
+
+    public Interpreter(Project project) {
+        this.project = project;
+    }
+    
+    public InterpreterValue run(String className, String methodName, List<InterpreterValue> arguments) {
+        val clazz = project.findClass(className);
+        val method = find(clazz.getMethods(),
+            method -> method.getName().equals(methodName));
+        val stackFrame = buildStackFrame(method, arguments);
+        
+        for (val statement : method.getBody()) {
+            val result = statement.accept(new Executor(new Evaluator(stackFrame)));
+            if (result.isPresent()) {
+                return result.get();
+            }
+        }
+        return UNIT;
+    }
+
+    private Map<Integer, InterpreterValue> buildStackFrame(
+        final MethodNode method,
+        List<InterpreterValue> arguments) {
+        
+        if (method.getArguments().size() != arguments.size()) {
+            throw new WrongNumberOfArguments(method.getArguments().size(), arguments.size());
+        }
+        
+        return IntStream.range(0, method.getArguments().size())
+            .boxed()
+            .collect(toMap(
+                index -> method.getArguments().get(index).getId(),
+                index -> arguments.get(index)));
+    }
+    
+    private class Executor implements StatementNodeVisitor<Optional<InterpreterValue>> {
+        private Evaluator evaluator;
+
+        public Executor(Evaluator evaluator) {
+            this.evaluator = evaluator;
+        }
+        
+        @Override
+        public Optional<InterpreterValue> visit(ReturnNode returnNode) {
+            return Optional.of(evaluator.eval(returnNode.getValue()));
+        }
+
+        @Override
+        public Optional<InterpreterValue> visit(ExpressionStatementNode expressionStatement) {
+            evaluator.eval(expressionStatement.getExpression());
+            return Optional.empty();
+        }
+    }
+    
+    private 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;
+        }
+    }
+}