As part of the Dynamo project for which I developed the Active View Walls at Plan View Level custom node, I also needed to be able to operate on straight Walls and radiused Walls separately. I ended up making a custom node to handle this, to both make the main graph easier to read and so that I could easily reuse the "code" should I need to do this in a different graph in the future.
The graph of the custom node is fairly straightforward, as you can see in the image below. (Click on any reduced-size image to see the image full size.)
While my current application passes this node a list of Walls, I decided that may not always be the case in future graphs, so the first set of nodes uses a RemoveIfNot node to strip out any element in the list that is not a Wall.
While poking around in the properties that were available on the Walls in my test project, I noticed that radiused Walls have a parameter called Center Mark Visible, while straight Walls do not. When getting the parameter value for Center Mark Visible, straight Walls will have an empty string value, while radiused Walls will have a value of 0 (center mark not visible) or 1 (center mark visible). I chose to use this as the way to determine if a Wall was straight or radiused. The next set of nodes generates a list of Booleans (true or false) that parallels the list of Walls. The corresponding Boolean will be true if the Center Mark Visible parameter value for the Wall is an empty string (straight Wall) or false if the value is not an empty string (radiused Wall).
The list of Booleans generated by the previous set of nodes is used as a "Boolean mask" by a List.FilterByBoolMask node and applied to the list of Walls to generate two separate lists. The "in" list contains all of the Walls with a corresponding Boolean of true, or all of the straight Walls. The "out" list contains all of the Walls with a corresponding Boolean of false, or all of the radiused Walls.
The in and out lists are connected to the Straight and Curved outputs of the custom node, so that the main graph has access to the two filtered lists. This custom node was developed in Dynamo 0.8.2, but has been successfully used in the 0.9.1 and 1.0.0 versions as well.