Thans Gregory, But I sticked to the original solution because the exercise was about primitive recursion and pattern matching over lists.
Gregory Propf wrote: > > Well there's this approach. Granted you need to split the input list into > *both* args of the fold (i.e. the "input list" is really [1,4,5,3] but you > can get this with head and tail). I'm just learning about the fold family > myself. - Greg > > Prelude> foldl (\a b -> if (any (\x -> x == b) a) then a else b:a) [1] > [4,5,3,3,4] > [3,5,4,1] > > > > ----- Original Message ---- > From: Alexteslin <[EMAIL PROTECTED]> > To: haskell-cafe@haskell.org > Sent: Tuesday, July 10, 2007 1:40:56 PM > Subject: [Haskell-cafe] function unique > > > Hi, i am a beginner to Haskell and i have a beginner's question to ask. > > An exercise asks to define function unique :: [Int] -> [Int], which > outputs > a list with only elements that are unique to the input list (that appears > no > more than once). I defined a function with list comprehension which works > but trying to implement with pattern matching and primitive recursion with > lists and doesn't work. > > unique :: [Int] -> [Int] > unique xs = [x | x <- xs, elemNum2 x xs == 1] > > > elemNum2 :: Int -> [Int] -> Int > elemNum2 el xs = length [x| x <- xs, x == el] > > //This doesn't work, I know because the list shrinks and produces wrong > result but can not get a right //thinking > > unique2 :: [Int] -> [Int] > unique2 [] = [] > unique2 (x:xs) > |elemNum2 x xs == 1 = x:unique2 xs > |otherwise = unique2 xs > > > Any help to a right direction would be very appreciated, thanks. > -- > View this message in context: > http://www.nabble.com/function-unique-tf4058328.html#a11528933 > 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 > > > > > > > > > ____________________________________________________________________________________ > Shape Yahoo! in your own image. Join our Network Research Panel today! > http://surveylink.yahoo.com/gmrs/yahoo_panel_invite.asp?a=7 > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- View this message in context: http://www.nabble.com/function-unique-tf4058328.html#a11543175 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
