Initial commit

31 files changed, 585 insertions, 0 deletions

diff --git a/.classpath b/.classpath
new file mode 100644
index 0000000..a67b19b
--- /dev/null
+++ b/.classpath
@@ -0,0 +1,22 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="src" output="target/classes" path="src/main/java">
+		<attributes>
+			<attribute name="optional" value="true"/>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="src" output="target/test-classes" path="src/test/java">
+		<attributes>
+			<attribute name="optional" value="true"/>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8"/>
+	<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
+		<attributes>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="output" path="target/classes"/>
+</classpath>
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/.project b/.project
new file mode 100644
index 0000000..b727570
--- /dev/null
+++ b/.project
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>couscous</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.m2e.core.maven2Builder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+		<nature>org.eclipse.m2e.core.maven2Nature</nature>
+	</natures>
+</projectDescription>
diff --git a/.settings/org.eclipse.core.resources.prefs b/.settings/org.eclipse.core.resources.prefs
new file mode 100644
index 0000000..f9fe345
--- /dev/null
+++ b/.settings/org.eclipse.core.resources.prefs
@@ -0,0 +1,4 @@
+eclipse.preferences.version=1
+encoding//src/main/java=UTF-8
+encoding//src/test/java=UTF-8
+encoding/<project>=UTF-8
diff --git a/.settings/org.eclipse.jdt.core.prefs b/.settings/org.eclipse.jdt.core.prefs
new file mode 100644
index 0000000..6e80039
--- /dev/null
+++ b/.settings/org.eclipse.jdt.core.prefs
@@ -0,0 +1,8 @@
+eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=enabled
+org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.8
+org.eclipse.jdt.core.compiler.compliance=1.8
+org.eclipse.jdt.core.compiler.problem.assertIdentifier=error
+org.eclipse.jdt.core.compiler.problem.enumIdentifier=error
+org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
+org.eclipse.jdt.core.compiler.source=1.8
diff --git a/.settings/org.eclipse.m2e.core.prefs b/.settings/org.eclipse.m2e.core.prefs
new file mode 100644
index 0000000..f897a7f
--- /dev/null
+++ b/.settings/org.eclipse.m2e.core.prefs
@@ -0,0 +1,4 @@
+activeProfiles=
+eclipse.preferences.version=1
+resolveWorkspaceProjects=true
+version=1
diff --git a/pom.xml b/pom.xml
new file mode 100644
index 0000000..204af41
--- /dev/null
+++ b/pom.xml
@@ -0,0 +1,37 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.zwobble.couscous</groupId>
+  <artifactId>couscous</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+  <packaging>jar</packaging>
+
+  <name>couscous</name>
+  <url>http://maven.apache.org</url>
+
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.12</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.projectlombok</groupId>
+      <artifactId>lombok</artifactId>
+      <version>1.16.6</version>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.google.guava</groupId>
+      <artifactId>guava</artifactId>
+      <version>18.0</version>
+      <scope>runtime</scope>
+    </dependency>
+  </dependencies>
+</project>
diff --git a/src/main/java/org/zwobble/couscous/Project.java b/src/main/java/org/zwobble/couscous/Project.java
new file mode 100644
index 0000000..6afac6e
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/Project.java
@@ -0,0 +1,7 @@
+package org.zwobble.couscous;
+
+import org.zwobble.couscous.ast.ClassNode;
+
+public interface Project {
+    ClassNode findClass(String name);
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/Assignment.java b/src/main/java/org/zwobble/couscous/ast/Assignment.java
new file mode 100644
index 0000000..aa7f89b
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/Assignment.java
@@ -0,0 +1,16 @@
+package org.zwobble.couscous.ast;
+
+import org.zwobble.couscous.ast.visitors.ExpressionNodeVisitor;
+
+import lombok.Value;
+
+@Value
+public class Assignment implements ExpressionNode {
+    VariableReferenceNode target;
+    ExpressionNode value;
+    
+    @Override
+    public <T> T accept(ExpressionNodeVisitor<T> visitor) {
+        return visitor.visit(this);
+    }
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/CallNode.java b/src/main/java/org/zwobble/couscous/ast/CallNode.java
new file mode 100644
index 0000000..d71c891
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/CallNode.java
@@ -0,0 +1,5 @@
+package org.zwobble.couscous.ast;
+
+public class CallNode {
+
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/ClassNode.java b/src/main/java/org/zwobble/couscous/ast/ClassNode.java
new file mode 100644
index 0000000..ffa5165
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/ClassNode.java
@@ -0,0 +1,14 @@
+package org.zwobble.couscous.ast;
+
+import java.util.List;
+
+import lombok.Builder;
+import lombok.Singular;
+import lombok.Value;
+
+@Builder
+@Value
+public class ClassNode {
+    @Singular
+    List<MethodNode> methods;
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/ExpressionNode.java b/src/main/java/org/zwobble/couscous/ast/ExpressionNode.java
new file mode 100644
index 0000000..097377a
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/ExpressionNode.java
@@ -0,0 +1,7 @@
+package org.zwobble.couscous.ast;
+
+import org.zwobble.couscous.ast.visitors.ExpressionNodeVisitor;
+
+public interface ExpressionNode {
+    <T> T accept(ExpressionNodeVisitor<T> visitor);
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/ExpressionStatementNode.java b/src/main/java/org/zwobble/couscous/ast/ExpressionStatementNode.java
new file mode 100644
index 0000000..ec04663
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/ExpressionStatementNode.java
@@ -0,0 +1,15 @@
+package org.zwobble.couscous.ast;
+
+import org.zwobble.couscous.ast.visitors.StatementNodeVisitor;
+
+import lombok.Value;
+
+@Value
+public class ExpressionStatementNode implements StatementNode {
+    ExpressionNode expression;
+
+    @Override
+    public <T> T accept(StatementNodeVisitor<T> visitor) {
+        return visitor.visit(this);
+    }
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/FormalArgumentNode.java b/src/main/java/org/zwobble/couscous/ast/FormalArgumentNode.java
new file mode 100644
index 0000000..da3a838
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/FormalArgumentNode.java
@@ -0,0 +1,9 @@
+package org.zwobble.couscous.ast;
+
+import lombok.Value;
+
+@Value
+public class FormalArgumentNode implements VariableNode {
+    int id;
+    String name;
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/LiteralNode.java b/src/main/java/org/zwobble/couscous/ast/LiteralNode.java
new file mode 100644
index 0000000..38688d8
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/LiteralNode.java
@@ -0,0 +1,26 @@
+package org.zwobble.couscous.ast;
+
+import org.zwobble.couscous.ast.visitors.ExpressionNodeVisitor;
+import org.zwobble.couscous.values.IntegerValue;
+import org.zwobble.couscous.values.InterpreterValue;
+import org.zwobble.couscous.values.StringValue;
+
+import lombok.Value;
+
+@Value
+public class LiteralNode implements ExpressionNode {
+    public static LiteralNode of(String value) {
+        return new LiteralNode(new StringValue(value));
+    }
+    
+    public static LiteralNode of(int value) {
+        return new LiteralNode(new IntegerValue(value));
+    }
+    
+    InterpreterValue value;
+
+    @Override
+    public <T> T accept(ExpressionNodeVisitor<T> visitor) {
+        return visitor.visit(this);
+    }
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/MethodNode.java b/src/main/java/org/zwobble/couscous/ast/MethodNode.java
new file mode 100644
index 0000000..91acbd5
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/MethodNode.java
@@ -0,0 +1,22 @@
+package org.zwobble.couscous.ast;
+
+import java.util.List;
+
+import lombok.Builder;
+import lombok.Singular;
+import lombok.Value;
+
+@Builder
+@Value
+public class MethodNode {
+    public static MethodNodeBuilder staticMethod(String name) {
+        return builder().isStatic(true).name(name);
+    }
+    
+    boolean isStatic;
+    String name;
+    @Singular
+    List<FormalArgumentNode> arguments; 
+    @Singular("statement")
+    List<StatementNode> body;
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/ReturnNode.java b/src/main/java/org/zwobble/couscous/ast/ReturnNode.java
new file mode 100644
index 0000000..529dbb5
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/ReturnNode.java
@@ -0,0 +1,15 @@
+package org.zwobble.couscous.ast;
+
+import org.zwobble.couscous.ast.visitors.StatementNodeVisitor;
+
+import lombok.Value;
+
+@Value
+public class ReturnNode implements StatementNode {
+    ExpressionNode value;
+
+    @Override
+    public <T> T accept(StatementNodeVisitor<T> visitor) {
+        return visitor.visit(this);
+    }
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/StatementNode.java b/src/main/java/org/zwobble/couscous/ast/StatementNode.java
new file mode 100644
index 0000000..773420e
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/StatementNode.java
@@ -0,0 +1,7 @@
+package org.zwobble.couscous.ast;
+
+import org.zwobble.couscous.ast.visitors.StatementNodeVisitor;
+
+public interface StatementNode {
+    <T> T accept(StatementNodeVisitor<T> visitor); 
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/VariableNode.java b/src/main/java/org/zwobble/couscous/ast/VariableNode.java
new file mode 100644
index 0000000..4c689c5
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/VariableNode.java
@@ -0,0 +1,5 @@
+package org.zwobble.couscous.ast;
+
+public interface VariableNode {
+    int getId();
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/VariableReferenceNode.java b/src/main/java/org/zwobble/couscous/ast/VariableReferenceNode.java
new file mode 100644
index 0000000..536a7c3
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/VariableReferenceNode.java
@@ -0,0 +1,19 @@
+package org.zwobble.couscous.ast;
+
+import org.zwobble.couscous.ast.visitors.ExpressionNodeVisitor;
+
+import lombok.Value;
+
+@Value
+public class VariableReferenceNode implements ExpressionNode {
+    public static VariableReferenceNode reference(VariableNode variable) {
+        return new VariableReferenceNode(variable.getId());
+    }
+    
+    int referentId;
+
+    @Override
+    public <T> T accept(ExpressionNodeVisitor<T> visitor) {
+        return visitor.visit(this);
+    }
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/visitors/ExpressionNodeVisitor.java b/src/main/java/org/zwobble/couscous/ast/visitors/ExpressionNodeVisitor.java
new file mode 100644
index 0000000..0167abc
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/visitors/ExpressionNodeVisitor.java
@@ -0,0 +1,11 @@
+package org.zwobble.couscous.ast.visitors;
+
+import org.zwobble.couscous.ast.Assignment;
+import org.zwobble.couscous.ast.LiteralNode;
+import org.zwobble.couscous.ast.VariableReferenceNode;
+
+public interface ExpressionNodeVisitor<T> {
+    T visit(LiteralNode literal);
+    T visit(VariableReferenceNode variableReference);
+    T visit(Assignment assignment);
+}
diff --git a/src/main/java/org/zwobble/couscous/ast/visitors/StatementNodeVisitor.java b/src/main/java/org/zwobble/couscous/ast/visitors/StatementNodeVisitor.java
new file mode 100644
index 0000000..6cec404
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/ast/visitors/StatementNodeVisitor.java
@@ -0,0 +1,9 @@
+package org.zwobble.couscous.ast.visitors;
+
+import org.zwobble.couscous.ast.ExpressionStatementNode;
+import org.zwobble.couscous.ast.ReturnNode;
+
+public interface StatementNodeVisitor<T> {
+    T visit(ReturnNode returnNode);
+    T visit(ExpressionStatementNode expressionStatement);
+}
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;
+        }
+    }
+}
diff --git a/src/main/java/org/zwobble/couscous/interpreter/InterpreterException.java b/src/main/java/org/zwobble/couscous/interpreter/InterpreterException.java
new file mode 100644
index 0000000..d6d7020
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/InterpreterException.java
@@ -0,0 +1,6 @@
+package org.zwobble.couscous.interpreter;
+
+public class InterpreterException extends RuntimeException {
+    private static final long serialVersionUID = 1L;
+
+}
diff --git a/src/main/java/org/zwobble/couscous/interpreter/WrongNumberOfArguments.java b/src/main/java/org/zwobble/couscous/interpreter/WrongNumberOfArguments.java
new file mode 100644
index 0000000..06d8079
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/interpreter/WrongNumberOfArguments.java
@@ -0,0 +1,13 @@
+package org.zwobble.couscous.interpreter;
+
+import lombok.EqualsAndHashCode;
+import lombok.Value;
+
+@Value
+@EqualsAndHashCode(callSuper=false)
+public class WrongNumberOfArguments extends InterpreterException {
+    private static final long serialVersionUID = 1L;
+    
+    int expected;
+    int actual;
+}
diff --git a/src/main/java/org/zwobble/couscous/values/IntegerValue.java b/src/main/java/org/zwobble/couscous/values/IntegerValue.java
new file mode 100644
index 0000000..062d137
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/values/IntegerValue.java
@@ -0,0 +1,8 @@
+package org.zwobble.couscous.values;
+
+import lombok.Value;
+
+@Value
+public class IntegerValue implements InterpreterValue {
+    int value;
+}
diff --git a/src/main/java/org/zwobble/couscous/values/InterpreterValue.java b/src/main/java/org/zwobble/couscous/values/InterpreterValue.java
new file mode 100644
index 0000000..64b0e91
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/values/InterpreterValue.java
@@ -0,0 +1,5 @@
+package org.zwobble.couscous.values;
+
+public interface InterpreterValue {
+
+}
diff --git a/src/main/java/org/zwobble/couscous/values/StringValue.java b/src/main/java/org/zwobble/couscous/values/StringValue.java
new file mode 100644
index 0000000..1478d41
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/values/StringValue.java
@@ -0,0 +1,8 @@
+package org.zwobble.couscous.values;
+
+import lombok.Value;
+
+@Value
+public class StringValue implements InterpreterValue {
+    String value;
+}
diff --git a/src/main/java/org/zwobble/couscous/values/UnitValue.java b/src/main/java/org/zwobble/couscous/values/UnitValue.java
new file mode 100644
index 0000000..1cf9dc7
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/values/UnitValue.java
@@ -0,0 +1,11 @@
+package org.zwobble.couscous.values;
+
+import lombok.ToString;
+
+@ToString
+public class UnitValue implements InterpreterValue {
+    public static final UnitValue UNIT = new UnitValue(); 
+    
+    private UnitValue() {
+    }
+}
diff --git a/src/test/java/org/zwobble/couscous/tests/interpreter/InterpreterTests.java b/src/test/java/org/zwobble/couscous/tests/interpreter/InterpreterTests.java
new file mode 100644
index 0000000..d3bc21c
--- /dev/null
+++ b/src/test/java/org/zwobble/couscous/tests/interpreter/InterpreterTests.java
@@ -0,0 +1,117 @@
+package org.zwobble.couscous.tests.interpreter;
+
+import java.util.Map;
+
+import org.junit.Test;
+import org.zwobble.couscous.Project;
+import org.zwobble.couscous.ast.Assignment;
+import org.zwobble.couscous.ast.ClassNode;
+import org.zwobble.couscous.ast.ExpressionStatementNode;
+import org.zwobble.couscous.ast.FormalArgumentNode;
+import org.zwobble.couscous.ast.LiteralNode;
+import org.zwobble.couscous.ast.MethodNode;
+import org.zwobble.couscous.ast.ReturnNode;
+import org.zwobble.couscous.interpreter.Interpreter;
+import org.zwobble.couscous.interpreter.WrongNumberOfArguments;
+import org.zwobble.couscous.values.InterpreterValue;
+import org.zwobble.couscous.values.StringValue;
+
+import com.google.common.collect.ImmutableMap;
+
+import static java.util.Arrays.asList;
+import static org.junit.Assert.assertEquals;
+import static org.zwobble.couscous.ast.MethodNode.staticMethod;
+import static org.zwobble.couscous.ast.VariableReferenceNode.reference;
+import static org.zwobble.couscous.tests.util.ExtraAsserts.assertThrows;
+import static org.zwobble.couscous.values.UnitValue.UNIT;
+
+import lombok.val;
+
+public class InterpreterTests {
+    @Test
+    public void canReturnLiteralValue() {
+        val method = staticMethod("hello")
+            .statement(new ReturnNode(LiteralNode.of("hello, world!")));
+        val result = runMethod(method);
+        
+        assertEquals(new StringValue("hello, world!"), result);
+    }
+    
+    @Test
+    public void canPassValueToMethod() {
+        val arg = new FormalArgumentNode(42, "x");
+        val method = staticMethod("hello")
+            .argument(arg)
+            .statement(new ReturnNode(reference(arg)));
+        val result = runMethod(method, new StringValue("hello, world!"));
+        
+        assertEquals(new StringValue("hello, world!"), result);
+    }
+    
+    @Test
+    public void errorIfWrongNumberOfArgumentsArePassed() {
+        val method = staticMethod("hello");
+        
+        val exception = assertThrows(WrongNumberOfArguments.class,
+            () -> runMethod(method, new StringValue("hello, world!")));
+        
+        assertEquals(new WrongNumberOfArguments(0, 1), exception);
+    }
+    
+    @Test
+    public void canReassignValueToArgument() {
+        val arg = new FormalArgumentNode(42, "x");
+        val method = staticMethod("hello")
+            .argument(arg)
+            .statement(new ExpressionStatementNode(new Assignment(reference(arg), LiteralNode.of("[updated value]"))))
+            .statement(new ReturnNode(reference(arg)));
+        val result = runMethod(method, new StringValue("[initial value]"));
+        
+        assertEquals(new StringValue("[updated value]"), result);
+    }
+    
+    @Test
+    public void valueOfAssignmentExpressionIsNewValue() {
+        val arg = new FormalArgumentNode(42, "x");
+        val method = staticMethod("hello")
+            .argument(arg)
+            .statement(new ReturnNode(new Assignment(reference(arg), LiteralNode.of("[updated value]"))));
+        val result = runMethod(method, new StringValue("[initial value]"));
+        
+        assertEquals(new StringValue("[updated value]"), result);
+    }
+    
+    @Test
+    public void methodWithNoStatementsReturnsUnit() {
+        val method = staticMethod("hello");
+        val result = runMethod(method);
+        
+        assertEquals(UNIT, result);
+    }
+
+    private InterpreterValue runMethod(MethodNode.MethodNodeBuilder methodBuilder, InterpreterValue... arguments) {
+        val method = methodBuilder.build();
+        val classNode = ClassNode.builder()
+            .method(method)
+            .build();
+        val className = "com.example.Program";
+        val interpreter = new Interpreter(new MapBackedProject(ImmutableMap.of(
+            className, classNode)));
+        
+        return interpreter.run(className, method.getName(), asList(arguments));
+    }
+
+    private static class MapBackedProject implements Project {
+        private Map<String, ClassNode> classes;
+
+        public MapBackedProject(Map<String, ClassNode> classes) {
+            this.classes = classes;
+        }
+        
+        @Override
+        public ClassNode findClass(String name) {
+            return classes.get(name);
+        }
+        
+    }
+}
diff --git a/src/test/java/org/zwobble/couscous/tests/util/ExtraAsserts.java b/src/test/java/org/zwobble/couscous/tests/util/ExtraAsserts.java
new file mode 100644
index 0000000..8b1c16c
--- /dev/null
+++ b/src/test/java/org/zwobble/couscous/tests/util/ExtraAsserts.java
@@ -0,0 +1,21 @@
+package org.zwobble.couscous.tests.util;
+
+public class ExtraAsserts {
+    public interface Action {
+        void run();
+    }
+    
+    @SuppressWarnings("unchecked")
+    public static <T extends Throwable> T assertThrows(Class<T> exceptionType, Action action) {
+        try {
+            action.run();
+            throw new AssertionError("Expected exception");
+        } catch (Exception exception) {
+            if (exceptionType.isInstance(exception)) {
+                return (T)exception;
+            } else {
+                throw exception;
+            }
+        }
+    }
+}