Hi, In the foldl library, the definition of Handler <http://hackage.haskell.org/package/foldl-1.2.0/docs/Control-Foldl.html#t:Handler> is:
type Handler a b = forall x. (b -> Const <http://hackage.haskell.org/package/base-4.8.2.0/docs/Control-Applicative.html#t:Const> (Dual <http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-Monoid.html#t:Dual> (Endo <http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-Monoid.html#t:Endo> x)) b) -> a -> Const <http://hackage.haskell.org/package/base-4.8.2.0/docs/Control-Applicative.html#t:Const> (Dual <http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-Monoid.html#t:Dual> (Endo <http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-Monoid.html#t:Endo> x)) a It resembles the definition of a lens/traversal/fold, but what does the Dual <http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-Monoid.html#t:Dual> (Endo <http://hackage.haskell.org/package/base-4.8.2.0/docs/Data-Monoid.html#t:Endo> x) part do? -- You received this message because you are subscribed to the Google Groups "Haskell Pipes" group. To unsubscribe from this group and stop receiving emails from it, send an email to haskell-pipes+unsubscr...@googlegroups.com. To post to this group, send email to haskell-pipes@googlegroups.com.
