Then you might want to use something like:

currentTimeStr :: IO String
currentTimeStr = do ct <- currentTime
                    return ("File creation date: " ++ show ct ++ " by MyCompany")

Or more concisely,

currentTimeStr :: IO String
currentTimeStr = liftM (\ ct -> "File creation date: " ++ show ct ++ " by MyCompany" ) currentTime

My point is, the type of currentTimeStr is IO String, not just String. Because you are working on an IO value.

Best,

PS: If you are not confident with the piece of code I've suggested, please have a look at the io/monads/do-notation sections of the Real World Haskell.

On 24 June 2010 11:17, Luca Ciciriello <luca_ciciriello@hotmail.com> wrote:

Starting from the beginning, my original problem is to create the string:

"File creation date:  " ++ currentSystemDate ++ " by MyCompany"

to obtain the string

"File creation date: 2010-06-24 by MyCompany"

Probably this is really trivial, but I'm a real beginner in Haskell and this seems to me a big problem.

Luca.

On Jun 24, 2010, at 9:59 AM, Ozgur Akgun wrote:

On 24 June 2010 10:52, Luca Ciciriello <luca_ciciriello@hotmail.com> wrote:

Just a question.
How can I obtain a String from

currentTime :: IO Day
currentTime =  utctDay `fmap` getCurrentTime

Here currentTime returns to me 2010-06-24, but I want "2010-06-24".
In another worlds I need a function

I bet Day has a Show instance (that's why you get 2010-06-24 in ghci I suppose)
Just use that.

 

currentTimeStr :: IO Day -> String

Getting out of IO? I would think again. Following might be what you really want:

currentTimeStr :: IO Day -> IO String

 

Any Idea?

Luca.

 
Best,
Ozgur

--
Ozgur Akgun