I cannot see a problem with parentheses in my build.boot. In fact, I am pasting from other published solutions, and they all suffer the same problem when I try to use them.
I struggle with hoplon - my existing file doesn't compile so, I shall try another example, from scratch, and see if I can compile that.
Otherwise, I'm going to throw my hands up, and put Hoplon behind me - it seems to be taking up a lot of time, without reward.
Also, the community has gone very quiet - are they ahead of me in my thinking, or progressing nicely and too busy to answer boner questions? Certainly, my experiences don't seem to be widely shared.