Thanks! The lightbulb just came on and I figured that out. Compose segment 1, segment 2, segment 1 mirrored (although the mirroring isn't obvious right now, it will be)
I'm modiffying that one you looked at for me before to make tower blocks of height based on the spline ID. The corners will always be balconies, with the rest one of three segment types, including balconies, arranged in rows using that nested generator method you showed me.
Do you know of a way I can ensure those composed coner segments always get the same map from a Railclone color map? The interior lights will be self illuminating textures via a Railclone colour, but it would be good if both side of the corner look cohesive - i.e. get assigned the same map. You can see below that's not currently the case.
Also is the something like an auto-tidy for the graph like in Max's SME? My graph is a mess!