Why isn't TBQueue backed by an array?

[konsumlamm]

I expected TBQueue to be backed by an array, instead of a pair of lists. This would get rid of the amortization and should cause less allocations. Have there been any benchmarks showing that the current version is faster?

[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.