[Haskell-beginners] mayBe stuck

[aditya siram]

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

On Thu, Aug 5, 2010 at 5:31 PM, aditya siram <aditya.siram at gmail.com> wrote:

> This is happening because findIndex has the signature:
> findIndex<http://hackage.haskell.org/packages/archive/haskell98/latest/doc/html/List.html#v:findIndex>:: (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.html
>
>
> On Thu, Aug 5, 2010 at 5:22 PM, prad <prad at towardsfreedom.com> 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 at haskell.org
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.haskell.org/pipermail/beginners/attachments/20100805/810c79aa/attachment-0001.html