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:readFi... "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:fromIn... (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