Hi, studying IO with files, i got this tutorial program. By the way, i discover the Data.Map module. Several questions then come to my mind : q1: why, in mapM_, make (sort (keys grades)) ? keys is already sorted, isn't it? q2: why, in mapM_, have grades twice (in draw then keys). I wonder if writing only draw grades, one could then extract the s and g parts in the draw function (via keys and elems). From this, i have problems with the type of grades; which is it? The insert function, using insertWith should give Map k a, but foldr seems to change this (couldn't match expected type [Map k a] against inferred type Map [String] a1 on the mapM_ line . q3: To solve the types problem, I tried to debug : i can get the types for s, marks and avg but for g, it says not in scope. How can i get this information ? q4: I also tried to type the parameter in draw (draw (x::Map k a) = ...) but i got an error : Illegal signature in pattern use -XScopedTypeVariables to permit it Since this parameter is visibly not set by default in ghci, is it a good idea to set it ? Thanks and happy new year. Didier import Data.Char <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Char> import Data.Maybe <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Maybe> import Data.List import Data.Map hiding (map <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:map>) import Text.Printf main = do src <- readFile <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:readFile> "grades" let pairs = map <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:map> (split.words <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:words>) (lines <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:lines> src) let grades = foldr <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:foldr> insert empty pairs mapM_ <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:mapM_> (draw grades) (sort (keys grades)) where insert (s, g) = insertWith (++ <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:.>) s [g] split [name,mark] = (name, read <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:read> mark) draw g s = printf "%s\t%s\tAverage: %f\n" s (show <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:show> marks) avg where marks = findWithDefault (error <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:error> "No such student") s g avg = sum <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:sum> marks / fromIntegral <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:fromIntegral> (length <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:length> marks) :: Double <http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Double>