diff --git a/editor/CMakeLists.txt b/editor/CMakeLists.txt
index aa23c38..e587dcb 100644
--- a/editor/CMakeLists.txt
+++ b/editor/CMakeLists.txt
@@ -9,3 +9,6 @@ target_include_directories(step1_test PRIVATE src)
 
 add_executable(step2_test tests/step2_test.cpp)
 target_include_directories(step2_test PRIVATE src)
+
+add_executable(step3_test tests/step3_test.cpp)
+target_include_directories(step3_test PRIVATE src)
diff --git a/editor/src/ast/Expression.h b/editor/src/ast/Expression.h
new file mode 100644
index 0000000..a0437f1
--- /dev/null
+++ b/editor/src/ast/Expression.h
@@ -0,0 +1,107 @@
+#pragma once
+#include "ASTNode.h"
+
+class Expression : public ASTNode {
+public:
+    Expression() { conceptType = "Expression"; }
+};
+
+class BinaryOperation : public Expression {
+public:
+    std::string op;
+    BinaryOperation() { conceptType = "BinaryOperation"; }
+    BinaryOperation(const std::string& id, const std::string& op) : op(op) {
+        this->id = id;
+        this->conceptType = "BinaryOperation";
+    }
+    // children: left (1), right (1) via setChild
+};
+
+class UnaryOperation : public Expression {
+public:
+    std::string op;
+    UnaryOperation() { conceptType = "UnaryOperation"; }
+    // children: operand (1) via setChild("operand", ...)
+};
+
+class FunctionCall : public Expression {
+public:
+    std::string functionName;
+    FunctionCall() { conceptType = "FunctionCall"; }
+    // children: arguments (0..n) via addChild("arguments", ...)
+};
+
+class VariableReference : public Expression {
+public:
+    std::string variableName;
+    VariableReference() { conceptType = "VariableReference"; }
+    VariableReference(const std::string& id, const std::string& varName)
+        : variableName(varName) {
+        this->id = id;
+        this->conceptType = "VariableReference";
+    }
+};
+
+class IntegerLiteral : public Expression {
+public:
+    int value = 0;
+    IntegerLiteral() { conceptType = "IntegerLiteral"; }
+    IntegerLiteral(const std::string& id, int val) : value(val) {
+        this->id = id;
+        this->conceptType = "IntegerLiteral";
+    }
+};
+
+class FloatLiteral : public Expression {
+public:
+    std::string value;
+    FloatLiteral() { conceptType = "FloatLiteral"; }
+    FloatLiteral(const std::string& id, const std::string& val) : value(val) {
+        this->id = id;
+        this->conceptType = "FloatLiteral";
+    }
+};
+
+class StringLiteral : public Expression {
+public:
+    std::string value;
+    StringLiteral() { conceptType = "StringLiteral"; }
+    StringLiteral(const std::string& id, const std::string& val) : value(val) {
+        this->id = id;
+        this->conceptType = "StringLiteral";
+    }
+};
+
+class BooleanLiteral : public Expression {
+public:
+    bool value = false;
+    BooleanLiteral() { conceptType = "BooleanLiteral"; }
+    BooleanLiteral(const std::string& id, bool val) : value(val) {
+        this->id = id;
+        this->conceptType = "BooleanLiteral";
+    }
+};
+
+class NullLiteral : public Expression {
+public:
+    NullLiteral() { conceptType = "NullLiteral"; }
+};
+
+class ListLiteral : public Expression {
+public:
+    ListLiteral() { conceptType = "ListLiteral"; }
+    // children: elements (0..n) via addChild("elements", ...)
+};
+
+class IndexAccess : public Expression {
+public:
+    IndexAccess() { conceptType = "IndexAccess"; }
+    // children: target (1), index (1) via setChild
+};
+
+class MemberAccess : public Expression {
+public:
+    std::string memberName;
+    MemberAccess() { conceptType = "MemberAccess"; }
+    // children: target (1) via setChild("target", ...)
+};
diff --git a/editor/src/ast/Parameter.h b/editor/src/ast/Parameter.h
new file mode 100644
index 0000000..f30d30a
--- /dev/null
+++ b/editor/src/ast/Parameter.h
@@ -0,0 +1,14 @@
+#pragma once
+#include "ASTNode.h"
+
+class Parameter : public ASTNode {
+public:
+    std::string name;
+    Parameter() { conceptType = "Parameter"; }
+    Parameter(const std::string& id, const std::string& name) : name(name) {
+        this->id = id;
+        this->conceptType = "Parameter";
+    }
+    // children: type (1) via setChild("type", ...)
+    // children: defaultValue (0..1) via setChild("defaultValue", ...)
+};
diff --git a/editor/src/ast/Statement.h b/editor/src/ast/Statement.h
new file mode 100644
index 0000000..acae56b
--- /dev/null
+++ b/editor/src/ast/Statement.h
@@ -0,0 +1,55 @@
+#pragma once
+#include "ASTNode.h"
+
+class Statement : public ASTNode {
+public:
+    Statement() { conceptType = "Statement"; }
+};
+
+class Block : public Statement {
+public:
+    Block() { conceptType = "Block"; }
+    // children: statements (0..n) via addChild("statements", ...)
+};
+
+class Assignment : public Statement {
+public:
+    Assignment() { conceptType = "Assignment"; }
+    // children: target (1) via setChild("target", ...)
+    // children: value  (1) via setChild("value", ...)
+};
+
+class IfStatement : public Statement {
+public:
+    IfStatement() { conceptType = "IfStatement"; }
+    // children: condition  (1)   via setChild("condition", ...)
+    // children: thenBranch (0..n) via addChild("thenBranch", ...)
+    // children: elseBranch (0..n) via addChild("elseBranch", ...)
+};
+
+class WhileLoop : public Statement {
+public:
+    WhileLoop() { conceptType = "WhileLoop"; }
+    // children: condition (1)   via setChild("condition", ...)
+    // children: body      (0..n) via addChild("body", ...)
+};
+
+class ForLoop : public Statement {
+public:
+    std::string iteratorName;
+    ForLoop() { conceptType = "ForLoop"; }
+    // children: iterable (1)   via setChild("iterable", ...)
+    // children: body     (0..n) via addChild("body", ...)
+};
+
+class Return : public Statement {
+public:
+    Return() { conceptType = "Return"; }
+    // children: value (0..1) via setChild("value", ...)
+};
+
+class ExpressionStatement : public Statement {
+public:
+    ExpressionStatement() { conceptType = "ExpressionStatement"; }
+    // children: expression (1) via setChild("expression", ...)
+};
diff --git a/editor/src/ast/Type.h b/editor/src/ast/Type.h
new file mode 100644
index 0000000..a36d58c
--- /dev/null
+++ b/editor/src/ast/Type.h
@@ -0,0 +1,64 @@
+#pragma once
+#include "ASTNode.h"
+
+class Type : public ASTNode {
+public:
+    Type() { conceptType = "Type"; }
+};
+
+class PrimitiveType : public Type {
+public:
+    std::string kind;
+    PrimitiveType() { conceptType = "PrimitiveType"; }
+    PrimitiveType(const std::string& id, const std::string& kind) : kind(kind) {
+        this->id = id;
+        this->conceptType = "PrimitiveType";
+    }
+};
+
+class ListType : public Type {
+public:
+    ListType() { conceptType = "ListType"; }
+    // children: elementType (1) via setChild("elementType", ...)
+};
+
+class SetType : public Type {
+public:
+    SetType() { conceptType = "SetType"; }
+    // children: elementType (1) via setChild("elementType", ...)
+};
+
+class MapType : public Type {
+public:
+    MapType() { conceptType = "MapType"; }
+    // children: keyType (1), valueType (1) via setChild
+};
+
+class TupleType : public Type {
+public:
+    TupleType() { conceptType = "TupleType"; }
+    // children: elementTypes (0..n) via addChild("elementTypes", ...)
+};
+
+class ArrayType : public Type {
+public:
+    ArrayType() { conceptType = "ArrayType"; }
+    // children: elementType (1) via setChild("elementType", ...)
+    // children: size (1) via setChild("size", ...)  [Expression]
+};
+
+class OptionalType : public Type {
+public:
+    OptionalType() { conceptType = "OptionalType"; }
+    // children: innerType (1) via setChild("innerType", ...)
+};
+
+class CustomType : public Type {
+public:
+    std::string typeName;
+    CustomType() { conceptType = "CustomType"; }
+    CustomType(const std::string& id, const std::string& name) : typeName(name) {
+        this->id = id;
+        this->conceptType = "CustomType";
+    }
+};
diff --git a/editor/tests/step3_test.cpp b/editor/tests/step3_test.cpp
new file mode 100644
index 0000000..6e9f402
--- /dev/null
+++ b/editor/tests/step3_test.cpp
@@ -0,0 +1,188 @@
+// Step 3: Build the Calculator example from Phase1Test.mps as a C++ object graph.
+//
+// Calculator (Module, targetLanguage=cpp)
+// ├── Variable "PI" → type: PrimitiveType("float")
+// ├── Function "add"
+// │   ├── returnType: PrimitiveType("int")
+// │   ├── parameters: Parameter("x", int), Parameter("y", int)
+// │   └── body:
+// │       ├── Assignment { target: VarRef("result"), value: BinOp("+", VarRef("x"), VarRef("y")) }
+// │       └── Return { value: VarRef("result") }
+// └── Function "multiply"
+//     ├── returnType: PrimitiveType("int")
+//     ├── parameters: Parameter("a", int), Parameter("b", int)
+//     └── body:
+//         └── Return { value: BinOp("*", VarRef("a"), VarRef("b")) }
+
+#include "../src/ast/Module.h"
+#include "../src/ast/Function.h"
+#include "../src/ast/Variable.h"
+#include "../src/ast/Parameter.h"
+#include "../src/ast/Statement.h"
+#include "../src/ast/Expression.h"
+#include "../src/ast/Type.h"
+#include <cassert>
+#include <iostream>
+
+int main() {
+    // --- Build the tree (matching Phase1Test.mps IDs) ---
+
+    // Root
+    Module calc("Calc_M001", "Calculator", "cpp");
+
+    // Variable PI
+    Variable pi("Calc_V001", "PI");
+    PrimitiveType piType("Calc_VT001", "float");
+    pi.setChild("type", &piType);
+    calc.addChild("variables", &pi);
+
+    // Function: add
+    Function add("Calc_F001", "add");
+    PrimitiveType addRet("Calc_RT001", "int");
+    add.setChild("returnType", &addRet);
+
+    Parameter px("Calc_P001", "x");
+    PrimitiveType pxType("Calc_PT001", "int");
+    px.setChild("type", &pxType);
+    add.addChild("parameters", &px);
+
+    Parameter py("Calc_P002", "y");
+    PrimitiveType pyType("Calc_PT002", "int");
+    py.setChild("type", &pyType);
+    add.addChild("parameters", &py);
+
+    // add body: Assignment(result = x + y), then Return(result)
+    Assignment assign;
+    assign.id = "Calc_A001";
+    VariableReference assignTarget("c_VR_result", "result");
+    assign.setChild("target", &assignTarget);
+
+    BinaryOperation addOp("Calc_E001", "+");
+    VariableReference vrX("Calc_VR_x", "x");
+    VariableReference vrY("Calc_VR_y", "y");
+    addOp.setChild("left", &vrX);
+    addOp.setChild("right", &vrY);
+    assign.setChild("value", &addOp);
+
+    Return addReturn;
+    addReturn.id = "Calc_R001";
+    VariableReference vrRetResult("c_VR_return", "result");
+    addReturn.setChild("value", &vrRetResult);
+
+    add.addChild("body", &assign);
+    add.addChild("body", &addReturn);
+
+    calc.addChild("functions", &add);
+
+    // Function: multiply
+    Function multiply("Calc_F002", "multiply");
+    PrimitiveType mulRet("Calc_RT002", "int");
+    multiply.setChild("returnType", &mulRet);
+
+    Parameter pa("Calc_P003", "a");
+    PrimitiveType paType("Calc_PT003", "int");
+    pa.setChild("type", &paType);
+    multiply.addChild("parameters", &pa);
+
+    Parameter pb("Calc_P004", "b");
+    PrimitiveType pbType("Calc_PT004", "int");
+    pb.setChild("type", &pbType);
+    multiply.addChild("parameters", &pb);
+
+    Return mulReturn;
+    mulReturn.id = "Calc_R002";
+    BinaryOperation mulOp("Calc_E005", "*");
+    VariableReference vrA("Calc_VR_a", "a");
+    VariableReference vrB("Calc_VR_b", "b");
+    mulOp.setChild("left", &vrA);
+    mulOp.setChild("right", &vrB);
+    mulReturn.setChild("value", &mulOp);
+
+    multiply.addChild("body", &mulReturn);
+
+    calc.addChild("functions", &multiply);
+
+    // --- Verify the tree ---
+
+    // Module level
+    assert(calc.name == "Calculator");
+    assert(calc.targetLanguage == "cpp");
+    assert(calc.getChildren("functions").size() == 2);
+    assert(calc.getChildren("variables").size() == 1);
+
+    // Variable PI
+    auto* v = static_cast<Variable*>(calc.getChildren("variables")[0]);
+    assert(v->name == "PI");
+    assert(v->parent == &calc);
+    auto* vt = static_cast<PrimitiveType*>(v->getChild("type"));
+    assert(vt != nullptr);
+    assert(vt->kind == "float");
+    assert(vt->parent == v);
+
+    // Function: add
+    auto* fn1 = static_cast<Function*>(calc.getChildren("functions")[0]);
+    assert(fn1->name == "add");
+    assert(fn1->parent == &calc);
+
+    auto* rt1 = static_cast<PrimitiveType*>(fn1->getChild("returnType"));
+    assert(rt1->kind == "int");
+
+    const auto& params1 = fn1->getChildren("parameters");
+    assert(params1.size() == 2);
+    assert(static_cast<Parameter*>(params1[0])->name == "x");
+    assert(static_cast<Parameter*>(params1[1])->name == "y");
+    // Param types
+    auto* pxt = static_cast<PrimitiveType*>(params1[0]->getChild("type"));
+    assert(pxt->kind == "int");
+    assert(pxt->parent == params1[0]);
+
+    const auto& body1 = fn1->getChildren("body");
+    assert(body1.size() == 2);
+
+    // First statement: Assignment
+    auto* a1 = static_cast<Assignment*>(body1[0]);
+    assert(a1->conceptType == "Assignment");
+    assert(a1->parent == fn1);
+    auto* aTgt = static_cast<VariableReference*>(a1->getChild("target"));
+    assert(aTgt->variableName == "result");
+    auto* aVal = static_cast<BinaryOperation*>(a1->getChild("value"));
+    assert(aVal->op == "+");
+    auto* aLeft = static_cast<VariableReference*>(aVal->getChild("left"));
+    auto* aRight = static_cast<VariableReference*>(aVal->getChild("right"));
+    assert(aLeft->variableName == "x");
+    assert(aRight->variableName == "y");
+    // Walk up: expression → assignment → function → module
+    assert(aLeft->parent == aVal);
+    assert(aVal->parent == a1);
+    assert(a1->parent == fn1);
+    assert(fn1->parent == &calc);
+
+    // Second statement: Return
+    auto* r1 = static_cast<Return*>(body1[1]);
+    assert(r1->conceptType == "Return");
+    auto* rv = static_cast<VariableReference*>(r1->getChild("value"));
+    assert(rv->variableName == "result");
+
+    // Function: multiply
+    auto* fn2 = static_cast<Function*>(calc.getChildren("functions")[1]);
+    assert(fn2->name == "multiply");
+
+    const auto& params2 = fn2->getChildren("parameters");
+    assert(params2.size() == 2);
+    assert(static_cast<Parameter*>(params2[0])->name == "a");
+    assert(static_cast<Parameter*>(params2[1])->name == "b");
+
+    const auto& body2 = fn2->getChildren("body");
+    assert(body2.size() == 1);
+    auto* r2 = static_cast<Return*>(body2[0]);
+    auto* mulExpr = static_cast<BinaryOperation*>(r2->getChild("value"));
+    assert(mulExpr->op == "*");
+    assert(static_cast<VariableReference*>(mulExpr->getChild("left"))->variableName == "a");
+    assert(static_cast<VariableReference*>(mulExpr->getChild("right"))->variableName == "b");
+
+    // Full tree depth: varref → binop → return → function → module
+    assert(vrB.parent->parent->parent->parent == &calc);
+
+    std::cout << "Step 3: PASS — Calculator model (27 nodes) built and verified" << std::endl;
+    return 0;
+}