diff --git a/latan/MathInterpreter.cpp b/latan/MathInterpreter.cpp
index 6025501..0fbc892 100644
--- a/latan/MathInterpreter.cpp
+++ b/latan/MathInterpreter.cpp
@@ -23,125 +23,13 @@
 using namespace std;
 using namespace Latan;
 
-/******************************************************************************
- *                        MathNode implementation                             *
- ******************************************************************************/
-// constructors ////////////////////////////////////////////////////////////////
-MathNode::MathNode(const string &name, const Type type)
-: name_(name)
-, type_(type)
-, parent_(nullptr)
-{}
-
-MathNode::MathNode(const std::string &name, const Type type,\
-                   const unsigned int nArg, ...)
-: name_(name)
-, type_(type)
-, arg_(nArg)
-, parent_(nullptr)
-{
-    va_list va;
-
-    va_start(va, nArg);
-    for (unsigned int i = 0; i < nArg; ++i)
-    {
-        arg_[i].reset(va_arg(va, MathNode *));
-        arg_[i]->parent_ = this;
-    }
-    va_end(va);
-}
-
-// destructor //////////////////////////////////////////////////////////////////
-MathNode::~MathNode(void)
-{}
-
-// access //////////////////////////////////////////////////////////////////////
-const string &MathNode::getName(void) const
-{
-    return name_;
-}
-
-MathNode::Type MathNode::getType(void) const
-{
-    return type_;
-}
-
-unsigned int MathNode::getNArg(void) const
-{
-    return static_cast<unsigned int>(arg_.size());
-}
-
-const MathNode * MathNode::getParent(void) const
-{
-    return parent_;
-}
-
-unsigned int MathNode::getLevel(void) const
-{
-    if (getParent())
-    {
-        return getParent()->getLevel() + 1;
-    }
-    else
-    {
-        return 0;
-    }
-}
-
-void MathNode::setName(const std::string &name)
-{
-    name_ = name;
-}
-
-void MathNode::pushArg(MathNode *node)
-{
-    arg_.push_back(unique_ptr<MathNode>(node));
-}
-
-// operators ///////////////////////////////////////////////////////////////////
-const MathNode &MathNode::operator[](const unsigned int i) const
-{
-    return *arg_[i];
-}
-
-ostream &Latan::operator<<(ostream &out, const MathNode &n)
-{
-    unsigned int level = n.getLevel();
-    
-    for (unsigned int i = 0; i <= level; ++i)
-    {
-        if (i == level)
-        {
-            out << "_";
-        }
-        else if (i == level - 1)
-        {
-            out << "|";
-        }
-        else
-        {
-            out << "  ";
-        }
-    }
-    out << " " << n.getName() << " (type " << static_cast<int>(n.getType())
-        << ")" << endl;
-    for (unsigned int i = 0; i < n.getNArg(); ++i)
-    {
-        out << n[i];
-    }
-    
-    return out;
-}
-
 /******************************************************************************
  *                            Instruction set                                 *
  ******************************************************************************/
 #define CODE_WIDTH 6
 #define CODE_MOD   setw(CODE_WIDTH) << left
 
-Instruction::~Instruction(void)
-{}
-
+// Instruction operator ////////////////////////////////////////////////////////
 ostream &Latan::operator<<(ostream& out, const Instruction& ins)
 {
     ins.print(out);
@@ -149,6 +37,7 @@ ostream &Latan::operator<<(ostream& out, const Instruction& ins)
     return out;
 }
 
+// Push constructors ///////////////////////////////////////////////////////////
 Push::Push(const double val)
 : type_(ArgType::Constant)
 , val_(val)
@@ -161,6 +50,7 @@ Push::Push(const string &name)
 , name_(name)
 {}
 
+// Push execution //////////////////////////////////////////////////////////////
 void Push::operator()(RunContext &context) const
 {
     if (type_ == ArgType::Constant)
@@ -181,6 +71,7 @@ void Push::operator()(RunContext &context) const
     context.insIndex++;
 }
 
+// Push print //////////////////////////////////////////////////////////////////
 void Push::print(ostream &out) const
 {
     out << CODE_MOD << "push";
@@ -194,10 +85,12 @@ void Push::print(ostream &out) const
     }
 }
 
+// Pop constructor /////////////////////////////////////////////////////////////
 Pop::Pop(const string &name)
 : name_(name)
 {}
 
+// Pop execution ///////////////////////////////////////////////////////////////
 void Pop::operator()(RunContext &context) const
 {
     if (!name_.empty())
@@ -208,15 +101,18 @@ void Pop::operator()(RunContext &context) const
     context.insIndex++;
 }
 
+// Pop print ///////////////////////////////////////////////////////////////////
 void Pop::print(ostream &out) const
 {
     out << CODE_MOD << "pop" << CODE_MOD << name_;
 }
 
+// Store constructor ///////////////////////////////////////////////////////////
 Store::Store(const string &name)
 : name_(name)
 {}
 
+// Store execution /////////////////////////////////////////////////////////////
 void Store::operator()(RunContext &context) const
 {
     if (!name_.empty())
@@ -226,15 +122,18 @@ void Store::operator()(RunContext &context) const
     context.insIndex++;
 }
 
+// Store print /////////////////////////////////////////////////////////////////
 void Store::print(ostream &out) const
 {
     out << CODE_MOD << "store" << CODE_MOD << name_;
 }
 
+// Call constructor ////////////////////////////////////////////////////////////
 Call::Call(const string &name)
 : name_(name)
 {}
 
+// Call execution //////////////////////////////////////////////////////////////
 void Call::operator()(RunContext &context) const
 {
     try
@@ -248,11 +147,13 @@ void Call::operator()(RunContext &context) const
     context.insIndex++;
 }
 
+// Call print //////////////////////////////////////////////////////////////////
 void Call::print(ostream &out) const
 {
     out << CODE_MOD << "call" << CODE_MOD << name_;
 }
 
+// Math operations /////////////////////////////////////////////////////////////
 #define DEF_OP(name, nArg, exp, insName)\
 void name::operator()(RunContext &context) const\
 {\
@@ -277,13 +178,199 @@ DEF_OP(Mul, 2, x[0]*x[1],      "mul")
 DEF_OP(Div, 2, x[0]/x[1],      "div")
 DEF_OP(Pow, 2, pow(x[0],x[1]), "pow")
 
+/******************************************************************************
+ *                        ExprNode implementation                             *
+ ******************************************************************************/
+// ExprNode constructors ///////////////////////////////////////////////////////
+ExprNode::ExprNode(const string &name)
+: name_(name)
+, parent_(nullptr)
+{}
+
+// ExprNode access /////////////////////////////////////////////////////////////
+const string &ExprNode::getName(void) const
+{
+    return name_;
+}
+
+unsigned int ExprNode::getNArg(void) const
+{
+    return static_cast<unsigned int>(arg_.size());
+}
+
+const ExprNode * ExprNode::getParent(void) const
+{
+    return parent_;
+}
+
+unsigned int ExprNode::getLevel(void) const
+{
+    if (getParent())
+    {
+        return getParent()->getLevel() + 1;
+    }
+    else
+    {
+        return 0;
+    }
+}
+
+void ExprNode::setName(const std::string &name)
+{
+    name_ = name;
+}
+
+void ExprNode::pushArg(ExprNode *node)
+{
+    if (node)
+    {
+        node->parent_ = this;
+        arg_.push_back(unique_ptr<ExprNode>(node));
+    }
+}
+
+// ExprNode operators //////////////////////////////////////////////////////////
+const ExprNode &ExprNode::operator[](const unsigned int i) const
+{
+    return *arg_[i];
+}
+
+ostream &Latan::operator<<(ostream &out, const ExprNode &n)
+{
+    unsigned int level = n.getLevel();
+    
+    for (unsigned int i = 0; i <= level; ++i)
+    {
+        if (i == level)
+        {
+            out << "_";
+        }
+        else if (i == level - 1)
+        {
+            out << "|";
+        }
+        else
+        {
+            out << "  ";
+        }
+    }
+    out << " " << n.getName() << endl;
+    for (unsigned int i = 0; i < n.getNArg(); ++i)
+    {
+        out << n[i];
+    }
+    
+    return out;
+}
+
+#define PUSH_INS(program, type, ...) \
+program.push_back(unique_ptr<type>(new type(__VA_ARGS__)))
+
+// VarNode compile /////////////////////////////////////////////////////////////
+void VarNode::compile(Program &program) const
+{
+    PUSH_INS(program, Push, getName());
+}
+
+// CstNode compile /////////////////////////////////////////////////////////////
+void CstNode::compile(Program &program) const
+{
+    PUSH_INS(program, Push, strTo<double>(getName()));
+}
+
+// SemicolonNode compile ///////////////////////////////////////////////////////
+void SemicolonNode::compile(Program &program) const
+{
+    auto &n = *this;
+    
+    for (unsigned int i = 0; i < getNArg(); ++i)
+    {
+        bool isAssign     = isDerivedFrom<AssignNode>(&n[i]);
+        bool isSemiColumn = isDerivedFrom<SemicolonNode>(&n[i]);
+        bool isKeyword    = isDerivedFrom<KeywordNode>(&n[i]);
+        
+        if (isAssign||isSemiColumn||isKeyword)
+        {
+            n[i].compile(program);
+        }
+    }
+}
+
+// AssignNode compile //////////////////////////////////////////////////////////
+void AssignNode::compile(Program &program) const
+{
+    auto &n = *this;
+    
+    if (isDerivedFrom<VarNode>(&n[0]))
+    {
+        bool hasSemicolonParent = isDerivedFrom<SemicolonNode>(getParent());
+        
+        n[1].compile(program);
+        if (hasSemicolonParent)
+        {
+            PUSH_INS(program, Pop, n[0].getName());
+        }
+        else
+        {
+            PUSH_INS(program, Store, n[0].getName());
+        }
+    }
+    else
+    {
+        LATAN_ERROR(Compilation, "invalid LHS for '='");
+    }
+}
+
+// MathOpNode compile //////////////////////////////////////////////////////////
+#define IFNODE(name, nArg) if ((n.getName() == (name))&&(n.getNArg() == nArg))
+#define ELIFNODE(name, nArg) else IFNODE(name, nArg)
+#define ELSE else
+
+void MathOpNode::compile(Program &program) const
+{
+    auto &n = *this;
+    
+    for (unsigned int i = 0; i < n.getNArg(); ++i)
+    {
+        n[i].compile(program);
+    }
+    IFNODE("-", 1)   PUSH_INS(program, Neg,);
+    ELIFNODE("+", 2) PUSH_INS(program, Add,);
+    ELIFNODE("-", 2) PUSH_INS(program, Sub,);
+    ELIFNODE("*", 2) PUSH_INS(program, Mul,);
+    ELIFNODE("/", 2) PUSH_INS(program, Div,);
+    ELIFNODE("^", 2) PUSH_INS(program, Pow,);
+    ELSE LATAN_ERROR(Compilation, "unknown operator '" + getName() + "'");
+}
+
+// FuncNode compile ////////////////////////////////////////////////////////////
+void FuncNode::compile(Program &program) const
+{
+    auto &n = *this;
+    
+    for (unsigned int i = 0; i < n.getNArg(); ++i)
+    {
+        n[i].compile(program);
+    }
+    PUSH_INS(program, Call, getName());
+}
+
+// ReturnNode compile ////////////////////////////////////////////////////////////
+void ReturnNode::compile(Program &program) const
+{
+    auto &n = *this;
+    
+    n[0].compile(program);
+    program.push_back(nullptr);
+}
+
 /******************************************************************************
  *                       MathInterpreter implementation                       *
  ******************************************************************************/
 // MathParserState constructor /////////////////////////////////////////////////
 MathInterpreter::MathParserState::MathParserState
-(istream *stream, string *name, std::unique_ptr<MathNode> *data)
-: ParserState<std::unique_ptr<MathNode>>(stream, name, data)
+(istream *stream, string *name, std::unique_ptr<ExprNode> *data)
+: ParserState<std::unique_ptr<ExprNode>>(stream, name, data)
 {
     initScanner();
 }
@@ -300,7 +387,6 @@ MathInterpreter::MathInterpreter(void)
 , codeName_("<no_code>")
 , state_(nullptr)
 , root_(nullptr)
-, gotReturn_(false)
 , status_(Status::none)
 {}
 
@@ -309,7 +395,6 @@ MathInterpreter::MathInterpreter(const std::string &code)
 , codeName_("<string>")
 , state_(nullptr)
 , root_(nullptr)
-, gotReturn_(false)
 , status_(Status::none)
 {
     setCode(code);
@@ -325,7 +410,7 @@ const Instruction * MathInterpreter::operator[](const unsigned int i) const
     return program_[i].get();
 }
 
-const MathNode * MathInterpreter::getAST(void) const
+const ExprNode * MathInterpreter::getAST(void) const
 {
     return root_.get();
 }
@@ -345,6 +430,7 @@ void MathInterpreter::setCode(const std::string &code)
     code_.reset(new stringstream(code));
     codeName_ = "<string>";
     state_.reset(new MathParserState(code_.get(), &codeName_, &root_));
+    program_.clear();
     status_   = Status::initialised;
 }
 
@@ -371,139 +457,36 @@ void MathInterpreter::parse(void)
 // interpreter /////////////////////////////////////////////////////////////////
 void MathInterpreter::compile(void)
 {
+    bool gotReturn = false;
+    
     if (!(status_ & Status::parsed))
     {
         parse();
         status_ |= Status::parsed;
         status_ -= status_ & Status::compiled;
     }
-    gotReturn_ = false;
     if (root_)
     {
-        compileNode(*root_);
+        root_->compile(program_);
+        for (unsigned int i = 0; i < program_.size(); ++i)
+        {
+            if (!program_[i])
+            {
+                gotReturn = true;
+                program_.resize(i);
+                program_.shrink_to_fit();
+                break;
+            }
+        }
+        
     }
-    if (!root_||!gotReturn_)
+    if (!root_||!gotReturn)
     {
         LATAN_ERROR(Syntax, "expected 'return' in program '" + codeName_ + "'");
     }
     status_ |= Status::compiled;
 }
 
-#define IFNODE(name, nArg) if ((n.getName() == (name))&&(n.getNArg() == nArg))
-#define ELIFNODE(name, nArg) else IFNODE(name, nArg)
-#define ELSE else
-
-#define PUSH_INS(type, ...) \
-program_.push_back(unique_ptr<type>(new (type)(__VA_ARGS__)))
-
-void MathInterpreter::compileNode(const MathNode& n)
-{
-    if (!gotReturn_)
-    {
-        switch (n.getType())
-        {
-            case MathNode::Type::cst:
-                PUSH_INS(Push, strTo<double>(n.getName()));
-                break;
-            case MathNode::Type::var:
-                PUSH_INS(Push, n.getName());
-                break;
-            case MathNode::Type::op:
-                // semicolon
-                if (n.getName() == ";")
-                {
-                    // compile relevant statements
-                    for (unsigned int i = 0; i < n.getNArg(); ++i)
-                    {
-                        bool isAssign =
-                        ((n[i].getType() == MathNode::Type::op)&&
-                         (n[i].getName() == "="));
-                        bool isSemiColumn =
-                        ((n[i].getType() == MathNode::Type::op)&&
-                         (n[i].getName() == ";"));
-                        bool isKeyword =
-                        (n[i].getType() == MathNode::Type::keyw);
-                        
-                        if (isAssign||isSemiColumn||isKeyword)
-                        {
-                            compileNode(n[i]);
-                        }
-                    }
-                }
-                // assignment
-                else if (n.getName() == "=")
-                {
-                    // variable assignement
-                    if (n[0].getType() == MathNode::Type::var)
-                    {
-                        bool hasSemicolonParent = ((n.getParent() != NULL) &&
-                                                   (n.getParent()->getType()
-                                                    == MathNode::Type::op)&&
-                                                   (n.getParent()->getName()
-                                                    == ";"));
-                        // compile the RHS
-                        compileNode(n[1]);
-                        // pop instruction if at the end of a statement
-                        if (hasSemicolonParent)
-                        {
-                            program_.push_back(unique_ptr<Pop>(new Pop(n[0].getName())));
-                        }
-                        // store instruction else
-                        else
-                        {
-                            PUSH_INS(Store, n[0].getName());
-                        }
-                    }
-                    else
-                    {
-                        LATAN_ERROR(Compilation, "invalid LHS for '='");
-                    }
-                }
-                // arithmetic operators
-                else
-                {
-                    for (unsigned int i = 0; i < n.getNArg(); ++i)
-                    {
-                        compileNode(n[i]);
-                    }
-                    IFNODE("-", 1)   PUSH_INS(Neg,);
-                    ELIFNODE("+", 2) PUSH_INS(Add,);
-                    ELIFNODE("-", 2) PUSH_INS(Sub,);
-                    ELIFNODE("*", 2) PUSH_INS(Mul,);
-                    ELIFNODE("/", 2) PUSH_INS(Div,);
-                    ELIFNODE("^", 2) PUSH_INS(Pow,);
-                    ELSE LATAN_ERROR(Compilation, "unknown operator '"
-                                     + n.getName() + "'");
-                }
-                break;
-            case MathNode::Type::keyw:
-                if (n.getName() == "return")
-                {
-                    compileNode(n[0]);
-                    gotReturn_ = true;
-                }
-                else
-                {
-                    LATAN_ERROR(Compilation, "unknown keyword '" + n.getName()
-                                + "'");
-                }
-                break;
-            case MathNode::Type::func:
-                for (unsigned int i = 0; i < n.getNArg(); ++i)
-                {
-                    compileNode(n[i]);
-                }
-                PUSH_INS(Call, n.getName());
-                break;
-            default:
-                LATAN_ERROR(Compilation,
-                            "unknown node type (node named '" + n.getName()
-                            + "')");
-                break;
-        }
-    }
-}
-
 // execution ///////////////////////////////////////////////////////////////////
 void MathInterpreter::operator()(RunContext &context)
 {
diff --git a/latan/MathInterpreter.hpp b/latan/MathInterpreter.hpp
index 39c67d9..b890fc5 100644
--- a/latan/MathInterpreter.hpp
+++ b/latan/MathInterpreter.hpp
@@ -33,47 +33,6 @@
 
 BEGIN_NAMESPACE
 
-/******************************************************************************
- *                            Expression node class                           *
- ******************************************************************************/
-class MathNode
-{
-public:
-    enum class Type
-    {
-        undef = -1,
-        cst   =  0,
-        op    =  1,
-        var   =  2,
-        keyw  =  3,
-        func  =  4
-    };
-public:
-    // constructors
-    MathNode(const std::string &name, const Type type);
-    MathNode(const std::string &name, const Type type,
-             const unsigned int nArg, ...);
-    // destructor
-    virtual ~MathNode();
-    // access
-    const std::string& getName(void)   const;
-    Type               getType(void)   const;
-    unsigned int       getNArg(void)   const;
-    const MathNode *   getParent(void) const;
-    unsigned int       getLevel(void)  const;
-    void               setName(const std::string &name);
-    void               pushArg(MathNode *node);
-    // operator
-    const MathNode &operator[](const unsigned int i) const;
-private:
-    std::string                             name_;
-    Type                                    type_;
-    std::vector<std::unique_ptr<MathNode>> arg_;
-    const MathNode *                        parent_;
-};
-
-std::ostream &operator<<(std::ostream &out, const MathNode &n);
-
 /******************************************************************************
  *                         Instruction classes                                *
  ******************************************************************************/
@@ -92,7 +51,8 @@ struct RunContext
 class Instruction
 {
 public:
-    virtual ~Instruction();
+    // destructor
+    virtual ~Instruction(void) = default;
     // instruction execution
     virtual void operator()(RunContext &context) const = 0;
     friend std::ostream & operator<<(std::ostream &out, const Instruction &ins);
@@ -102,6 +62,9 @@ private:
 
 std::ostream & operator<<(std::ostream &out, const Instruction &ins);
 
+// Instruction container
+typedef std::vector<std::unique_ptr<const Instruction>> Program;
+
 // Push
 class Push: public Instruction
 {
@@ -184,6 +147,59 @@ DECL_OP(Mul);
 DECL_OP(Div);
 DECL_OP(Pow);
 
+/******************************************************************************
+ *                            Expression node classes                         *
+ ******************************************************************************/
+class ExprNode
+{
+public:
+    // constructors
+    ExprNode(const std::string &name);
+    // destructor
+    virtual ~ExprNode() = default;
+    // access
+    const std::string& getName(void)   const;
+    unsigned int       getNArg(void)   const;
+    const ExprNode *   getParent(void) const;
+    unsigned int       getLevel(void)  const;
+    void               setName(const std::string &name);
+    void               pushArg(ExprNode *node);
+    // operator
+    const ExprNode &operator[](const unsigned int i) const;
+    // compile
+    virtual void compile(Program &program) const = 0;
+private:
+    std::string                             name_;
+    std::vector<std::unique_ptr<ExprNode>>  arg_;
+    const ExprNode *                        parent_;
+};
+
+std::ostream &operator<<(std::ostream &out, const ExprNode &n);
+
+#define DECL_NODE(base, name) \
+class name: public base\
+{\
+public:\
+    using base::base;\
+    virtual void compile(Program &program) const;\
+}
+
+DECL_NODE(ExprNode, VarNode);
+DECL_NODE(ExprNode, CstNode);
+DECL_NODE(ExprNode, SemicolonNode);
+DECL_NODE(ExprNode, AssignNode);
+DECL_NODE(ExprNode, MathOpNode);
+DECL_NODE(ExprNode, FuncNode);
+
+class KeywordNode: public ExprNode
+{
+public:
+    using ExprNode::ExprNode;
+    virtual void compile(Program &program) const = 0;
+};
+
+DECL_NODE(KeywordNode, ReturnNode);
+
 /******************************************************************************
  *                            Interpreter class                               *
  ******************************************************************************/
@@ -192,12 +208,12 @@ class MathInterpreter
 
 public:
     // parser state
-    class MathParserState: public ParserState<std::unique_ptr<MathNode>>
+    class MathParserState: public ParserState<std::unique_ptr<ExprNode>>
     {
     public:
         // constructor
         explicit MathParserState(std::istream *stream, std::string *name,
-                                 std::unique_ptr<MathNode> *data);
+                                 std::unique_ptr<ExprNode> *data);
         // destructor
         virtual ~MathParserState(void);
     private:
@@ -218,8 +234,6 @@ private:
             compiled    = 1 << 2
         };
     };
-    // instruction container
-    typedef std::vector<std::unique_ptr<const Instruction>> Program;
 public:
     // constructors
     MathInterpreter(void);
@@ -228,7 +242,7 @@ public:
     ~MathInterpreter(void);
     // access
     const Instruction * operator[](const unsigned int i) const;
-    const MathNode * getAST(void) const;
+    const ExprNode * getAST(void) const;
     // initialization
     void setCode(const std::string &code);
     // interpreter
@@ -246,15 +260,14 @@ private:
     // parser
     void parse(void);
     // interpreter
-    void compileNode(const MathNode &node);
+    void compileNode(const ExprNode &node);
     // execution
     void execute(RunContext &context) const;
 private:
     std::unique_ptr<std::istream>    code_;
     std::string                      codeName_;
     std::unique_ptr<MathParserState> state_;
-    std::unique_ptr<MathNode>        root_;
-    bool                             gotReturn_;
+    std::unique_ptr<ExprNode>        root_;
     Program                          program_;
     unsigned int                     status_;
 };
diff --git a/latan/MathParser.ypp b/latan/MathParser.ypp
index c1b834c..a55144a 100644
--- a/latan/MathParser.ypp
+++ b/latan/MathParser.ypp
@@ -42,7 +42,7 @@
 	double          val_double;
     char            val_char;
     char            val_str[MAXIDLENGTH];
-    Latan::MathNode *val_node;
+    Latan::ExprNode *val_node;
 }
 
 %token <val_char> ERR
@@ -70,6 +70,16 @@
             << locp->first_column << ": " << err;
         LATAN_ERROR(Parsing, buf.str());
 	}
+    
+    void _math_warning(YYLTYPE *locp, MathInterpreter::MathParserState *state,
+                       const char *err)
+	{
+        stringstream buf;
+        
+        buf << *(state->streamName) << ":" << locp->first_line << ":"\
+            << locp->first_column << ": " << err;
+        LATAN_WARNING(buf.str());
+	}
 
 	#define scanner state->scanner
 %}
@@ -83,16 +93,13 @@ program:
 
 stmt:
       ';'
-    {$$ = new MathNode(";", MathNode::Type::op, 0);}
+    {$$ = new SemicolonNode(";");}
     | expr ';'
-    {$$ = $1;}
+    {$$ = nullptr; _math_warning(&yylloc, state, "useless statement removed");}
     | ID '=' expr ';'
-    {
-        $$ = new MathNode("=", MathNode::Type::op, 2,              \
-                          new MathNode($ID,MathNode::Type::var), $3);
-    }
+    {$$ = new AssignNode("="); $$->pushArg(new VarNode($ID)); $$->pushArg($3);}
     | RETURN expr ';'
-    {$$ = new MathNode("return", MathNode::Type::keyw, 1, $2);}
+    {$$ = new ReturnNode("return"); $$->pushArg($2);}
     | '{' stmt_list '}'
     {$$ = $2;}
     ;
@@ -101,26 +108,26 @@ stmt_list:
       stmt
     {$$ = $1;}
     | stmt_list stmt
-    {$$ = new MathNode(";", MathNode::Type::op, 2, $1, $2);}
+    {$$ = new SemicolonNode(";"); $$->pushArg($1); $$->pushArg($2);}
     ;
 
 expr:
       FLOAT
-    {$$ = new MathNode($FLOAT, MathNode::Type::cst);}
+    {$$ = new CstNode($FLOAT);}
     | ID
-    {$$ = new MathNode($ID, MathNode::Type::var);}
+    {$$ = new VarNode($ID);}
     | '-' expr %prec UMINUS
-    {$$ = new MathNode("-", MathNode::Type::op, 1, $2);}
+    {$$ = new MathOpNode("-"); $$->pushArg($2);}
     | expr '+' expr
-    {$$ = new MathNode("+", MathNode::Type::op, 2, $1, $3);}
+    {$$ = new MathOpNode("+"); $$->pushArg($1); $$->pushArg($3);}
     | expr '-' expr
-    {$$ = new MathNode("-", MathNode::Type::op, 2, $1, $3);}
+    {$$ = new MathOpNode("-"); $$->pushArg($1); $$->pushArg($3);}
     | expr '*' expr
-    {$$ = new MathNode("*", MathNode::Type::op, 2, $1, $3);}
+    {$$ = new MathOpNode("*"); $$->pushArg($1); $$->pushArg($3);}
     | expr '/' expr
-    {$$ = new MathNode("/", MathNode::Type::op, 2, $1, $3);}
+    {$$ = new MathOpNode("/"); $$->pushArg($1); $$->pushArg($3);}
     | expr '^' expr
-    {$$ = new MathNode("^", MathNode::Type::op, 2, $1, $3);}
+    {$$ = new MathOpNode("^"); $$->pushArg($1); $$->pushArg($3);}
     | '(' expr ')'
     {$$ = $2;}
     | ID '(' func_args ')'
@@ -129,9 +136,9 @@ expr:
 
 func_args:
      /* empty string */
-    {$$ = new MathNode("", MathNode::Type::func);}
+    {$$ = new FuncNode("");}
     | expr
-    {$$ = new MathNode("", MathNode::Type::func, 1, $1);}
+    {$$ = new FuncNode(""); $$->pushArg($1);}
     | func_args ',' expr
     {$$ = $1; $$->pushArg($3);}
     ;