The function
show :: Show a => a -> String
can be used with
putStrLn :: String -> IO ()
to get the output on different lines.
The function
print :: Show a => a -> IO ()
print = putStr . show
-- convert to string and then print (without newline)
does not put a newline at the end, to get a newline you use
putStrLn . show $ ...
On 24 February 2015 at 15:14, Roelof Wobben
Yes, that is one of the books I have to read. For this exercises chapter 2 and 3 .
Roelof
Francesco Ariis schreef op 24-2-2015 om 10:37:
off list: try to give a more meaningful title to your posts (i.e. "cis194 help exercise 2" instead of "how to do this"). It might lead to more answers!
Also, have you tried "Learn you a haskell for great good"?
On Tue, Feb 24, 2015 at 10:28:28AM +0100, Roelof Wobben wrote:
Hello,
Im trying to solve exercise 2 of this course : http://www.seas.upenn.edu/~cis194/spring13/hw/02-ADTs.pdf
I have this till so far :
-- | Main entry point to the application. {-# OPTIONS_GHC -Wall #-}
module LogAnalysis where
import Data.Char (isDigit, isLetter) import Log
-- | checks if the String is of the format char int isValid :: String -> Bool isValid s = case words s of [a]:b:_ -> isLetter a && all isDigit b _ -> False
-- | Parse the String to make the right logmessage parse_line :: String -> LogMessage parse_line s = case words s of ("I":time:text) -> LogMessage Info (read time) (unwords text) ("W":time:text) -> LogMessage Warning (read time) (unwords text) ("E":errorcode:time:text) -> LogMessage (Error (read errorcode)) (read time) (unwords text) _ -> Unknown "This is not in the right format"
-- | here the actual function which uses isValid and parse to make the right log messages parseMessage :: String -> LogMessage parseMessage s = if isValid(s) then parse_line(s) else Unknown "This is not the right format"
parse :: String -> [logMessage] parse s = parse_line s
-- | The main entry point. main :: IO () main = do print $ show (parseMessage "I 4681 ehci 0xf43d000:15: regista14: [0xbffff 0xfed nosabled 00-02] Zonseres: brips byted nored)") print $ show (parseMessage "W 3654 e8] PGTT ASF! 00f00000003.2: 0x000 - 0000: 00009dbfffec00000: Pround/f1743colled") print $ show (parseMessage "E 47 1034 'What a pity it wouldn't stay!' sighed the Lory, as soon as it was quite")
But I do not see how I can get the output of the parse_line into a List.
Can anyone give me a tip ?
Roelof
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-- Regards Sumit Sahrawat