[Haskell-cafe] monads with take-out options

John Meacham john at repetae.net
Mon Nov 24 18:14:51 EST 2008

On Mon, Nov 24, 2008 at 02:06:33PM -0800, Greg Meredith wrote:
> Now, are there references for a theory of monads and take-out options? For
> example, it seems that all sensible notions of containers have take-out. Can
> we make the leap and define a container as a monad with a notion of
> take-out? Has this been done? Are there reasons for not doing? Can we say
> what conditions are necessary to ensure a notion of take-out?

Yes, you are describing 'co-monads'. 

here is an example that a quick web search brought up, and there was a
paper on them and their properties published a while ago

the duals in that version are

extract - return
duplicate - join
extend  - flip (>>=) (more or less)


John Meacham - ⑆repetae.net⑆john⑈

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