Why isn't `TBQueue` backed by an array?

[haskell]

Why isn't `TBQueue` backed by an array?

[bgamari]

I suppose you want something like the following?

data TBQueue a
   = TBQueue
        (TArray a) -- a ring buffer of entries
        (TVar Int) -- Index of first queued entry
        (TVar Int)  -- Index of last queued entry

This sounds plausible to me.

The implementation is likely as it is since no one has tried improving it. Do try writing an array based implementation and benchmark it against the current list-based approach.