The proposed definition has one drawback: it is strict in its second
argument.
It should be possible to make it lazy in its second argument while keeping
the single-pass behavior, though. Something like this?
ZipList xs <|> ZipList ys = ZipList $ go xs ys 0
where
go [] ys n = drop n ys
go (x:xs) ys n = x : (go xs ys $! n + 1)
On Tue, Jun 5, 2018, 15:36 박신환
Current definion of (<|>) for ZipLists:
ZipList http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ... xs http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ... <|> http://hackage.haskell.org/package/base-4.11.1.0/docs/src/GHC.Base.html#%3C%... ZipList http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ... ys http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ... = ZipList http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ... (xs http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ... ++ http://hackage.haskell.org/package/base-4.11.1.0/docs/src/GHC.Base.html#%2B%... drop http://hackage.haskell.org/package/base-4.11.1.0/docs/src/GHC.List.html#drop (length http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Data.Foldable.html... xs http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ...) ys http://hackage.haskell.org/package/base-4.11.1.0/docs/src/Control.Applicativ...)
doesn't work if the left argument is infinite. It should be:
ZipList [] <|> ys = ys xs <|> ZipList [] = xs ZipList (x:xs) <|> ZipList (_:ys) = ZipList (x : (ZipList xs <|> ZipList ys))
_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries