Re: [Haskell-beginners] function not working as expected, type issues

I didn't look closely enough at what you wrote, you had several issues. Let me try again: displayD :: String -> Int -> IO () displayD string 0 = return () displayD string count = do hPutStr stdout string displayD string (count - 1) This is one way to do it. You use the arguments themselves. Obviously this won't work with negative counts. displayD :: String -> Int -> IO () displayD string count | count <= 0 = return () | otherwise = do hPutStr stdout string displayD string (count - 1) And as for figuring out types. You should try to load your source file in ghci, and then use the :t and :i commands liberally to inspect functions you are using. You will begin to get the hang of it in no time. On Wed, Apr 9, 2014 at 2:08 AM, David McBride wrote:

Try using guards:

displayD :: IO () -> String -> Int displayD string count = | count > 0 = hPutStr stdout string | otherwise = displayD string (count - 1)

Alternatively use if, then, else.

On Wed, Apr 9, 2014 at 2:03 AM, Alexej Magura wrote:

...

K, so I have a function that I'm writing that takes a *string* and a *count* and prints the *string* to STDOUT *count* times:

displayD :: IO () -> String -> Int displayD string count = do (count > 0) && hPutStr stdout string (count > 0) && displayD string (count - 1)

However, when I try to compile the file, I get several errors; here's a pastebin: http://pastebin.com/DEsuAvfz

What I'm trying to do here is check to see if *count* is greater than 0, and then if it is, then I'd like to print *string* to STDOUT until *count* equals 0. I tried doing it via pattern matching, like so:

displayD string (count > 0) = do

But I haven't seen any examples of how to do pattern matching in functions using *do*, that is *IO*, so I'm unsure if the above is even anywhere near correct.

Still very uncomfortable with declaring function types: I have a hard time figuring out which type is returned and what type is expected as an arg. My initial guess is that the *first* type specified is the one returned, but I'm not sure.

-- Alexej Magura Sent with Airmail _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners