[Haskell-cafe] ZipList monad, anyone?

[Patai Gergely]

> Having spent several months on this exact problem, I'll say that I
> consider it pretty unlikely.
I wouldn't be very surprised if that was the case.

> A clever data structure might give you logarithmic or even amortized
> constant time access in sequential cases, but you probably will not have
> good garbage collection properties (all data will remain for all time).
I guess cleverness should be concentrated on aging streams properly. But
I do see how the ability to extract the diagonal conflicts with such
efforts.

> Stick with Applicative for this type of thing.  Monad will drive you
> insane :-)
In fact, even applicative is far from trivial. ;) For instance, I still
can't see how I could implement the <*> operator with stateless streams
that don't need to keep track of their local time (needed when combining
them with stateful streams, that is).

Gergely

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