[Haskell-cafe] Re: Data.Ring -- Pre-announce

Luke Palmer lrpalmer at gmail.com
Mon Jan 4 09:17:09 EST 2010

On Mon, Jan 4, 2010 at 6:51 AM, Maciej Piechotka <uzytkownik2 at gmail.com> wrote:
> About comonad - not exactly as every comonad is copointed and the only
> possible way is extract Empty = _|_

I think this module could be cleaned up by disallowing empty lists.
You have this nice semantic property that "every clist has a focus",
but when you add empty you have to add "unless it's empty".  focus
returns a Maybe, isEmpty is necessary.

I mean, it could be that your use case requires empty clists and would
be uglier without empty, but think about it.  I find in Haskell that
simplicity breeds simplicity; i.e. I'm willing to wager that whatever
algorithm you are using clist for will actually be cleaner if you got
rid of empty and modify the algorithm accordingly.  We shall see


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