Re: [Haskell-beginners] mayBe stuck

The problem was the use of 'i' in 'take' and drop both of which require a Int. Here is code that corrects that: import Data.List import Data.Maybe eqD = (=='%') test4 = let s = "zaoeu%aeuasnt%staashaeu%nthdanoe%nthd" in putStrLn $ show $ brS (findIndex eqD s) s brS :: Maybe Int -> String -> String brS i ss | isNothing i = ss | otherwise = (take (fromJust i) ss) ++ (brS newIndex newStr) where newIndex = findIndex eqD newStr newStr = drop ((fromJust i) +1) ss -deech On Thu, Aug 5, 2010 at 5:32 PM, aditya siram wrote:

Sorry didn't read that properly. Hold on. -deech

On Thu, Aug 5, 2010 at 5:31 PM, aditya siram wrote:

...

This is happening because findIndex has the signature: findIndexhttp://hackage.haskell.org/packages/archive/haskell98/latest/doc/html/List.h...:: (a -> Bool) -> [a] -> Maybe Int

From this we know that 'findIndex' can return a 'Just Int' or 'Nothing'.

GHC is telling you that you need to handle the case where the list element you ask for does not exist and findIndex returns 'Nothing'.

The functions in the Maybe module [1]may be of some help here.

-deech

[1] http://hackage.haskell.org/packages/archive/haskell98/latest/doc/html/Maybe....

On Thu, Aug 5, 2010 at 5:22 PM, prad wrote:

...

i'm trying to create my own split function with % as delimiter. so i have eqD = (=='%')

and send

let s = "zaoeu%aeuasnt%staashaeu%nthdanoe%nthd" putStrLn $ show $ brS (findIndex eqD s) s

to a function brS:

brS i ss | isNothing i = ss | otherwise = (take i ss) : (brS newIndex newStr) where newIndex = findIndex eqD newStr newStr = drop (i+1) ss

but get the following error:

Couldn't match expected type `Maybe a' against inferred type `Int' In the first argument of `isNothing', namely `i' In the expression: isNothing i :: mayBe a In a stmt of a pattern guard for the definition of `brS': isNothing i :: mayBe a

my understanding is that i need the isNothing because findIndex will return Just Int or Nothing.

however, i'm not sure how to resolve what seems to me to be an issue between a Maybe and an Int.

-- In friendship, prad

... with you on your journey Towards Freedom http://www.towardsfreedom.com (website) Information, Inspiration, Imagination - truly a site for soaring I's _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners