LambdaExpression visitor which reduces variables by transforming them to constants (if possible)

VariablesReductionVisitor.cs

public class VariablesReductionVisitor : ExpressionVisitor
{
    private List<Expression> _children;

    public override Expression Visit(Expression node)
    {
        // Preserve parent's child expressions collection
        var siblings = _children;
        _children = new List<Expression>();

        node = base.Visit(node);

        // If all the child expressions are constants then current one should be constant as well
        if (_children.Any() && _children.All(e => e == null || e is ConstantExpression))
        {
            // Evaluate expression locally
            node = Expression.Constant(Expression.Lambda(node).Compile().DynamicInvoke(), node.Type);
        }

        // Add to parent's child expressions collection
        if (siblings != null)
        {
            siblings.Add(node);
        }
        _children = siblings;

        return node;
    }
}