Hi Roelof,
The parse error is due to the colon ':' in the guards, where instead an
equals '=' should be used:
toDigits :: Integer -> [Integer]
toDigits n
| n < 0 = []
| otherwise = n/10 : []
You can see some more examples of the guard syntax under the heading
'Guards, guards!' in LYAH:
http://learnyouahaskell.com/syntax-in-functions#guards-guards
Hope that helps,
Brendan
On 5 February 2015 at 08:48, Roelof Wobben
Hello,
I have to do this :
Exercise 1 We need to first find the digits of a number. Define the functions toDigits :: Integer -> [Integer] toDigitsRev :: Integer -> [Integer] toDigits should convert positive Integers to a list of digits. (For 0 or negative inputs, toDigits should return the empty list.) toDigitsRev should do the same, but with the digits reversed. Example: toDigits 1234 == [1,2,3,4] Example: toDigitsRev 1234 == [4,3,2,1] Example: toDigits 0 == [] Example: toDigits (-17) == []
I have this so far :
-- | 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/10 : []
-- | Main entry point to the application. module Main where
-- | The main entry point. main :: IO () main = do toDigits 123
but now I see this error message :
src/Main.hs@5:3-5:4 parse error on input |
This is not homework because I do this as a self-study.
Roelof
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe