Thanks, Joel.
Putting the type IO [()] in the main declaration and this as the final line
of the main function does do the trick:
sequence [putStrLn $ show s | s <- newList]
But this is the kind of thing that makes Haskell types difficult for
beginners to work with...
Geoffrey
On Mon, Mar 9, 2015 at 4:15 PM, Joel Williamson wrote: main must have type IO a. Hoogle tells me that to convert [IO a] -> IO
[a], you should use the function sequence. Try applying that to your final
line. On Mon, 9 Mar 2015 16:07 Geoffrey Bays My main function looks like this: main :: [IO()]
main = do
let stud1 = Student {name = "Geoff", average = -99.0, grades =
[66,77,88]}
let stud2 = Student {name = "Doug", average = -99.0, grades =
[77,88,99]}
let stud3 = Student {name = "Ron", average = -99.0, grades =
[55,66,77]}
let studList = [stud1,stud2]
let newList = calcAvg studList
[putStrLn $ show s | s <- newList]
--putStrLn $ show (newList !! 0)
--putStrLn $ show (newList !! 1) With this final line, putStrLn $ show (newList !! 0), the type IO () in
the function declaration compiles fine.
But with [putStrLn $ show s | s <- newList] as the final line, [IO ()] in
the function declaration will not compile, I get this error: Couldn't match expected type `IO t0' with actual type `[IO ()]' What does the declared type need to be for a final line of:
[putStrLn $ show s | s <- newList] ??? Thanks, Geoffrey _______________________________________________
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