<*> for R is insufficiently lazy

[tomjaguarpaw]

L120 of R.hs should have a lazy pattern match, that is

(\b (Pair' x y) -> Pair' (bxx b x) (byy b y))

should read

(\b ~(Pair' x y) -> Pair' (bxx b x) (byy b y))

otherwise you cannot combine folds for infinite lists.

https://github.com/ekmett/folds/blob/d72e747bbbd7e2c7d967b575905a53c8c786adfa/src/Data/Fold/R.hs#L120

[tomjaguarpaw]

This came up on a Stack Overflow question about implementing unzip, however with further consideration perhaps it is rather perverse to try to implement unzip with a right fold, so feel free to summarily close the issue if I've missed the point of R.

[ekmett]

Missed this. (github rarely actually emails me, too may repos I guess.) If you want to dig through and find other laziness problems on the R or R1 front, I'm more than happy to merge changes there.