namespace Invercargill.Expressions {

    /**
     * Visitor interface for expression traversal and translation.
     * 
     * Implement this interface to traverse expression trees for purposes such as:
     * - SQL translation for ORM functionality
     * - Expression optimization
     * - Debugging/logging
     * - Validation
     * 
     * All methods have empty default implementations, so visitors only need
     * to override the methods they care about.
     */
    public interface ExpressionVisitor : Object {

        /**
         * Visit a literal expression.
         */
        public virtual void visit_literal(LiteralExpression expr) {}

        /**
         * Visit a variable expression.
         */
        public virtual void visit_variable(VariableExpression expr) {}

        /**
         * Visit a binary expression.
         */
        public virtual void visit_binary(BinaryExpression expr) {}

        /**
         * Visit a unary expression.
         */
        public virtual void visit_unary(UnaryExpression expr) {}

        /**
         * Visit a ternary expression.
         */
        public virtual void visit_ternary(TernaryExpression expr) {}

        /**
         * Visit a property expression.
         */
        public virtual void visit_property(PropertyExpression expr) {}

        /**
         * Visit a function call expression.
         */
        public virtual void visit_function_call(FunctionCallExpression expr) {}

        /**
         * Visit a lambda expression.
         */
        public virtual void visit_lambda(LambdaExpression expr) {}

        /**
         * Visit a bracketed expression.
         */
        public virtual void visit_bracketed(BracketedExpression expr) {}

    }

}