diff --git a/c-opopt.cc b/c-opopt.cc
index b1c9bb8..ef8198c 100644
--- a/c-opopt.cc
+++ b/c-opopt.cc
@@ -35,16 +35,33 @@ struct T_ConstantFolder_
 	bool operator()( A_Node& node , bool exit ) noexcept;
 
     private:
-	using F_ExprGet_ = std::function< A_ExpressionNode&( A_Node& ) >;
-	using F_ExprSet_ = std::function< void( A_Node& , P_ExpressionNode ) >;
-
-	void handleParentNode(
+	template<
+		typename T
+	> void handleParentNode(
 			A_Node& node ,
-			F_ExprGet_ get ,
-			F_ExprSet_ set ) noexcept;
+			std::function< A_ExpressionNode&( T& ) > get ,
+			std::function< void( T& , P_ExpressionNode ) > set ) noexcept;
 
 	P_ExpressionNode checkExpression(
-			A_ExpressionNode const& node ) noexcept;
+			A_ExpressionNode& node ) noexcept;
+
+	// Handle identifiers. If the size is fixed and the identifier is
+	// either width or height, replace it with the appropriate value.
+	P_ExpressionNode doIdExpr(
+			T_IdentifierExprNode& node ) noexcept;
+
+	// Transform an unary operator applied to a constant into a constant.
+	P_ExpressionNode doUnaryOp(
+			A_Node& parent ,
+			T_UnaryOperatorNode::E_Operator op ,
+			double value ) const noexcept;
+
+	// Transform a binary operator applied to a constant into a constant.
+	P_ExpressionNode doBinaryOp(
+			A_Node& parent ,
+			T_BinaryOperatorNode::E_Operator op ,
+			double left ,
+			double right ) const noexcept;
 };
 
 /*----------------------------------------------------------------------------*/
@@ -60,33 +77,24 @@ bool T_ConstantFolder_::operator()(
 	switch ( node.type( ) ) {
 
 	    case A_Node::TN_ARG:
-		handleParentNode( node ,
-			[]( A_Node& n ) -> A_ExpressionNode& {
-				return ((T_ArgumentNode&)n).expression( );
-			} ,
-			[]( A_Node& n , P_ExpressionNode e ) {
-				((T_ArgumentNode&)n).expression( std::move( e ) );
-			} );
+		handleParentNode< T_ArgumentNode >(
+			node ,
+			[]( auto& n ) -> A_ExpressionNode& { return n.expression( ); } ,
+			[]( auto& n , P_ExpressionNode e ) { n.expression( std::move( e ) ); }
+		);
 		return false;
 
 	    case A_Node::TN_CONDITION:
-		handleParentNode( node ,
-			[]( A_Node& n ) -> A_ExpressionNode& {
-				return ((T_CondInstrNode::T_Expression&)n).expression( );
-			} ,
-			[]( A_Node& n , P_ExpressionNode e ) {
-				((T_CondInstrNode::T_Expression&)n).expression( std::move( e ) );
-			} );
+		handleParentNode< T_CondInstrNode::T_Expression >( node ,
+			[]( auto& n ) -> A_ExpressionNode& { return n.expression( ); } ,
+			[]( auto& n , P_ExpressionNode e ) { n.expression( std::move( e ) ); }
+		);
 		return false;
 
 	    case A_Node::OP_SET:
-		handleParentNode( node ,
-			[]( A_Node& n ) -> A_ExpressionNode& {
-				return ((T_SetInstrNode&)n).expression( );
-			} ,
-			[]( A_Node& n , P_ExpressionNode e ) {
-				((T_SetInstrNode&)n).setExpression( std::move( e ) );
-			} );
+		handleParentNode< T_SetInstrNode >( node ,
+			[]( auto& n ) -> A_ExpressionNode& { return n.expression( ); } ,
+			[]( auto& n , P_ExpressionNode e ) { n.setExpression( std::move( e ) ); } );
 		return false;
 
 	    default:
@@ -94,56 +102,185 @@ bool T_ConstantFolder_::operator()(
 	}
 }
 
-void T_ConstantFolder_::handleParentNode(
-		A_Node& node ,
-		F_ExprGet_ get ,
-		F_ExprSet_ set ) noexcept
+/*----------------------------------------------------------------------------*/
+
+template<
+	typename T
+> void T_ConstantFolder_::handleParentNode(
+		A_Node& n ,
+		std::function< A_ExpressionNode&( T& ) > get ,
+		std::function< void( T& , P_ExpressionNode ) > set ) noexcept
 {
+	auto& node{ (T&) n };
 	auto r{ checkExpression( get( node ) ) };
 	if ( r ) {
+		r->location( ) = node.location( );
 		set( node , std::move( r ) );
 		didFold = true;
 	}
 }
 
-/*----------------------------------------------------------------------------*/
-
 P_ExpressionNode T_ConstantFolder_::checkExpression(
-		A_ExpressionNode const& node ) noexcept
+		A_ExpressionNode& node ) noexcept
 {
-#warning TODO optimize the fuck
-	// 1/ Replace inputs with value if no curve/constant curve
-	//    Replace $width/$height with value if fixedSize
-	// 2/ Replace UnOp( Cnst ) with result
-	//    Replace BinOp( Cnst , Cnst ) with result
-	// 3/ Try to find other optimisations, e.g. for Add( Cnst , Add( Cnst , Expr ) )
+	// Already a constant
+	if ( node.type( ) == A_Node::EXPR_CONST ) {
+		return {};
+	}
 
+	// Replace $width/$height with value if fixedSize
 	if ( node.type( ) == A_Node::EXPR_ID ) {
-		if ( !fixedSize ) {
-			return {};
-		}
+		return doIdExpr( (T_IdentifierExprNode&) node );
+	}
 
-		T_IdentifierExprNode& n{ (T_IdentifierExprNode&) node };
-		if ( n.id( ) == "width" ) {
-			auto c{ NewOwned< T_ConstantExprNode >( n.parent( ) ,
-					double( fixedSize->first ) ) };
-			c->location( ) = n.location( );
-			return c;
-		}
-		if ( n.id( ) == "height" ) {
-			auto c{ NewOwned< T_ConstantExprNode >( n.parent( ) ,
-					float( fixedSize->second ) ) };
-			c->location( ) = n.location( );
-			return c;
+	// Replace inputs with value if no curve/constant curve
+	if ( node.type( ) == A_Node::EXPR_INPUT ) {
+		// TODO: may be replaced with either a constant or a variable.
+		// * If the curve exists and describes a constant, it's a
+		// constant
+		// * If there is no curve and only one default value in the
+		// whole program then it's also a constant
+		// * No curve, multiple defaults -> variable
+		return {};
+	}
+
+	// Replace UnOp( Cnst ) with result
+	auto* const asUnary{ dynamic_cast< T_UnaryOperatorNode* >( &node ) };
+	if ( asUnary ) {
+		handleParentNode< T_UnaryOperatorNode >( *asUnary ,
+			[]( auto& n ) -> A_ExpressionNode& { return n.argument( ); } ,
+			[]( auto& n , P_ExpressionNode e ) { n.setArgument( std::move( e ) ); } );
+		if ( asUnary->argument( ).type( ) == A_Node::EXPR_CONST ) {
+			auto const& cn{ (T_ConstantExprNode const&) asUnary->argument( ) };
+			return doUnaryOp( asUnary->parent( ) , asUnary->op( ) ,
+					cn.floatValue( ) );
 		}
 		return {};
 	}
 
+	// Replace BinOp( Cnst , Cnst ) with result
+	auto* const asBinary{ dynamic_cast< T_BinaryOperatorNode* >( &node ) };
+	assert( asBinary && "Missing support for some expr subtype" );
+	handleParentNode< T_BinaryOperatorNode >( *asBinary ,
+		[]( auto& n ) -> A_ExpressionNode& { return n.left( ); } ,
+		[]( auto& n , P_ExpressionNode e ) { n.setLeft( std::move( e ) ); } );
+	handleParentNode< T_BinaryOperatorNode >( *asBinary ,
+		[]( auto& n ) -> A_ExpressionNode& { return n.right( ); } ,
+		[]( auto& n , P_ExpressionNode e ) { n.setRight( std::move( e ) ); } );
+
+	if ( asBinary->left( ).type( ) == A_Node::EXPR_CONST
+			&& asBinary->right( ).type( ) == A_Node::EXPR_CONST ) {
+		auto const& l{ (T_ConstantExprNode const&) asBinary->left( ) };
+		auto const& r{ (T_ConstantExprNode const&) asBinary->right( ) };
+		return doBinaryOp( asBinary->parent( ) , asBinary->op( ),
+				l.floatValue( ) , r.floatValue( ) );
+	}
+	return {};
+}
+
+/*----------------------------------------------------------------------------*/
+
+P_ExpressionNode T_ConstantFolder_::doIdExpr(
+		T_IdentifierExprNode& node ) noexcept
+{
+	if ( !fixedSize ) {
+		return {};
+	}
+
+	if ( node.id( ) == "width" ) {
+		return NewOwned< T_ConstantExprNode >( node.parent( ) ,
+				double( fixedSize->first ) );
+	}
+
+	if ( node.id( ) == "height" ) {
+		return NewOwned< T_ConstantExprNode >( node.parent( ) ,
+				float( fixedSize->second ) );
+	}
+
 	return {};
 }
 
+P_ExpressionNode T_ConstantFolder_::doUnaryOp(
+		A_Node& parent ,
+		const T_UnaryOperatorNode::E_Operator op ,
+		const double value ) const noexcept
+{
+	const double rVal{ []( const auto op , const auto value ) {
+		switch ( op ) {
+		    case T_UnaryOperatorNode::NEG:
+			return -value;
+		    case T_UnaryOperatorNode::NOT:
+			return value ? 0. : 1.;
+		    case T_UnaryOperatorNode::INV:
+			// TODO check if 0
+			return 1. / value;
+		    case T_UnaryOperatorNode::COS:
+			return cos( value );
+		    case T_UnaryOperatorNode::SIN:
+			return sin( value );
+		    case T_UnaryOperatorNode::TAN:
+			// TODO check if valid
+			return tan( value );
+		    case T_UnaryOperatorNode::SQRT:
+			// TODO check if >= 0
+			return sqrt( value );
+		    case T_UnaryOperatorNode::LN:
+			// TODO check if > 0
+			return log( value );
+		    case T_UnaryOperatorNode::EXP:
+			return exp( value );
+		}
+		fprintf( stderr , "invalid operator %d\n" , int( op ) );
+		std::abort( );
+	}( op , value ) };
+
+	return NewOwned< T_ConstantExprNode >( parent , rVal );
+}
+
+P_ExpressionNode T_ConstantFolder_::doBinaryOp(
+		A_Node& parent ,
+		const T_BinaryOperatorNode::E_Operator op ,
+		const double left ,
+		const double right ) const noexcept
+{
+	const double rVal{ []( const auto op , const auto l , const auto r ) {
+		switch ( op ) {
+		    case T_BinaryOperatorNode::ADD:
+			return l + r;
+		    case T_BinaryOperatorNode::SUB:
+			return l - r;
+		    case T_BinaryOperatorNode::MUL:
+			return l * r;
+		    case T_BinaryOperatorNode::DIV:
+			// TODO: check r != 0
+			return l / r;
+		    case T_BinaryOperatorNode::POW:
+			// TODO check operands
+			return pow( l , r );
+		    case T_BinaryOperatorNode::CMP_EQ:
+			return ( l == r ) ? 1. : 0.;
+		    case T_BinaryOperatorNode::CMP_NE:
+			return ( l != r ) ? 1. : 0.;
+		    case T_BinaryOperatorNode::CMP_GT:
+			return ( l > r ) ? 1. : 0.;
+		    case T_BinaryOperatorNode::CMP_GE:
+			return ( l >= r ) ? 1. : 0.;
+		    case T_BinaryOperatorNode::CMP_LT:
+			return ( l < r ) ? 1. : 0.;
+		    case T_BinaryOperatorNode::CMP_LE:
+			return ( l <= r ) ? 1. : 0.;
+		}
+		fprintf( stderr , "invalid operator %d\n" , int( op ) );
+		std::abort( );
+	}( op , left , right ) };
+
+	return NewOwned< T_ConstantExprNode >( parent , rVal );
+}
+
 } // namespace <anon>
 
+/*----------------------------------------------------------------------------*/
+
 
 bool opopt::FoldConstants(
 		T_RootNode& root ,