It's interesting that most of the Haskell solutions are somewhat similar

We did almost the exact same thing to the letter....

Kata changed as requested. Thanks for the feedback.

Well, I didn't read the instructions that carefully and I was a bit surprised. Perhaps there are others like me who already have an intuition of how regular expressions work, and who would be confused by the unusual precendences given in the instructions.

Yes. In the normal regular expressions concat has higher precedence than |. I specced the precedences bit unusual. I can change this, though it doesn't change much from the kata pov. The task is roughly the same.

Do you think it's worth changing the precedences now?

I would expect "ab|c" to be Or (Str [Normal 'a', Normal 'b']) (Normal 'c') and not `Str [Normal 'a', Or (Normal 'b') (Normal 'c')]