[Haskell-cafe] Problem using ap -- No instance for (Monad ((-) [[a]]))
If I try a function to make a point-free version of the function in this fold -- foldr (\x ys - ys ++ map (x:) ys) [[]] :pl gives me GOA Control.Monad :pl (\x ys - ys ++ map (x:) ys) ap (++) . map . (:) GOA Control.Monad :t ap (++) . map . (:) ap (++) . map . (:) :: (Monad ((-) [[a]])) = a - [[a]] - [[a]] but this is what happens if I try to use it: GOA Control.Monad let ps = foldr (ap (++) . map . (:)) [[]] interactive:1:16: No instance for (Monad ((-) [[a]])) arising from use of `ap' at interactive:1:16-22 Possible fix: add an instance declaration for (Monad ((-) [[a]])) In the first argument of `(.)', namely `ap (++)' In the first argument of `foldr', namely `((ap (++)) . (map . (:)))' In the expression: foldr ((ap (++)) . (map . (:))) [[]] (0.00 secs, 0 bytes) What gives? -- View this message in context: http://www.nabble.com/Problem-using-apNo-instance-for-%28Monad-%28%28-%3E%29---a--%29%29-tf4036243.html#a11466625 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem using ap -- No instance for (Monad ((-) [[a]]))
Hello Jim, Friday, July 6, 2007, 7:12:27 PM, you wrote: No instance for (Monad ((-) [[a]])) :l Control.Monad.Instances -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
