[Haskell-cafe] Stream fusion and span/break/group/init/tails

[Edward Z. Yang]

Hello all, (cc'd stream fusion paper authors)

I noticed that the current implementation of stream fusion does
not support "multiple-return" stream combinators, e.g.
break :: (a -> Bool) -> [a] -> ([a], [a]).  I thought a little
bit about how might one go about implement this, but the problem
seems nontrivial. (One possibility is to extend the definition
of Step to support multiple return, but the details are a mess!)
Nor, as far as I can tell, does the paper give any treatment of
the subject.  Has anyone thought about this subject in some detail?

Thanks,
Edward