Re: [Haskell-beginners] Couldn't match expected type ‘IO ()’ with actual type [Integer]

5 Feb 2015

      Max Voit schreef op 5-2-2015 om 13:35:
...
On Thu, 05 Feb 2015 13:25:16 +0100
Roelof Wobben  wrote:
...
Another question :  how can I display the array ?
putStrln works only for strings,
Yep, so you need to convert it to a string and putStrLn that. Kindly
enough typing ":i []" into ghci tells you, that lists have an instance
for "show".
Anonther option would be to convert every single list element to a
string and putStrLn that. "map" comes in handy here (or mapM_ if you
directly want to use print instead of putStrLn . show).
best,
Max
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Thanks that part worked fine.

One part I cannot figure out is how to make this :

-- | Main entry point to the application.
module Main where

-- | convert a number to a array in pieces where a negative number will 
be a empty array.
toDigits :: Integer -> [Integer]
toDigits n
   | n < 0 = []
   | otherwise = n `mod` 10 : []

-- | The main entry point.
main :: IO ()
main = do
     print $ toDigits 123

Now it showing only [1] or [23]
I have to find out how I can do something like this toDigits 23 [1]
But I cannot do this that way because it has to be Integer -> [Integer]

Who has a tip for me ?

Roelof