Thank you all for the responses.

Edward's objection is very serious, I didn't think of it.
Because of it I retract the proposal, this would indeed create big problems. (I just wish someone invents an oracle strictness analyzer...)

Instead, as suggested, I'll make a package with `newtype` wrappers for tuples that will provide the extra-lazy monoid semantics. Any ideas for what other type classes except `Monoid` (and `Semigroup`) could be included? Or perhaps even other data types except tuples?

Dne 08/18/2013 11:21 PM, Gabriel Gonzalez napsal(a):

I'm guessing this proposal is related to this Stack Overflow answer you gave:

http://stackoverflow.com/a/18289075/1026598

Note that your solution is very similar to the solution in the `foldl` package I just released (also based off of the same blog post you got your solution from).  The key differences are that:

* The `foldl` solution is for left folds and uses a strict tuple internally to prevent space leaks
* Your solution is for right folds and uses an extra-lazy tuple internally to promote laziness

This suggests to me that it would be better to keep this extra-lazy tuple as an internal implementation detail of a right-fold package that would be the lazy analogy of `foldl`, rather than modifying the standard Haskell tuple.

Yes, this is how I encountered the problem. If I have time I'll make a mirror package `foldr` based on extra-lazy tuples. (Or perhaps we could merge the ideas into a single package.)

  Best regards,
  Petr