On 24 February 2015 at 13:22, Roelof Wobben <r.wobben@home.nl> wrote:

Thanks,

I rewrote it like this :

parseMessage :: String -> LogMessage
parseMessage 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"

The code looks just fine. Great work.

The trouble is with the third case. The error message is fairly instructive.

log.hs:19:36:

Couldn't match expected type ‘String -> LogMessage’

with actual type ‘LogMessage’

The function ‘LogMessage’ is applied to four arguments,

but its type ‘MessageType -> TimeStamp -> String -> LogMessage’

has only three

In the expression:

LogMessage Error (read errorcode) (read time) (unwords text)

In a case alternative:

("E" : errorcode : time : text)

-> LogMessage Error (read errorcode) (read time) (unwords text)

log.hs:19:47:

Couldn't match expected type ‘MessageType’

with actual type ‘Int -> MessageType’

Probable cause: ‘Error’ is applied to too few arguments

In the first argument of ‘LogMessage’, namely ‘Error’

In the expression:

LogMessage Error (read errorcode) (read time) (unwords text)

Long story short, you meant to write

LogMessage (Error (read errorcode)) ...

instead of

LogMessage Error (read errorcode) ... -- Too many arguments to LogMessage (error message 1)

-- Too few arguments to Error (error message 2)

which is a very common error.