Sorry I wasn't clear. What I meant is that an idiomatic Haskell data structure needs to be persistent: an insertion needs to produce a new version of the data s

Sorry I wasn't clear. What I meant is that an idiomatic Haskell data structure needs to be persistent: an insertion needs to produce a new version of the data structure with the inserted element while keeping the original. So almost all Haskell data structures need to satisfy this requirement otherwise using it is a lot of PITA, even though the ST monad makes mutations fairly easy. However the original submission is not persistent, and so they aren't comparable.