[Haskell-cafe] How to print a string (lazily)
ndmitchell at gmail.com
Tue Jan 3 12:49:07 EST 2006
All Haskell functions are lazy, hence there is no need to "write a
lazy version" of your print_list function. I think the function you
probably want is:
putStr (unlines xs)
This uses the bulid in unlines function, which is similar in spirit to
join (you get more quotes, which I guess you don't want)
The equivalent in monad'y programming is:
mapM putStrLn xs
The first one has fewer monads, so I prefer it, but take your pick :)
On 1/3/06, Daniel Carrera <daniel.carrera at zmsl.com> wrote:
> I've been studying more Haskell and I've improved a lot. But I just hit
> a small problem. I want to print all the elements of a linst (putStr).
> I'd like to write something like this:
> print_list  = do putStr ""
> print_list (x:xs) = (do putStr x) && print_list xs
> I know this is wrong, but I hope you can see what I'm trying to do.
> I know of other ways I could print a list. For example:
> print_list xs = do putStr(join xs)
> where join  = ""
> join (x:xs) = (show x) ++ "\n" ++ join xs
> But the thing is, I want to write a lazy version of this function. It's
> not that I need such a function, I'm just trying to learn Haskell.
> Any suggestions?
> Question: What do you call a function that has side-effects? (like
> putStr) I know that "function" is the wrong term.
> /\/`) http://oooauthors.org
> /\/_/ http://opendocumentfellowship.org
> \/_/ I am not over-weight, I am under-tall.
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
More information about the Haskell-Cafe