[Haskell-cafe] parser error in pattern

[Ivan Lazar Miljenovic]

On 18 October 2011 09:14, kolli kolli <nammukolli04 at gmail.com> wrote:
> I didnt understand properly but made changes according to what I
> understood..Its still giving me the same error
>
> eval1(If t1 t2 t3) =  case (If t1 t2 t3) of
>                     eval1(If t1 t2 t3) ->  Just t1

You can't do that.... if you want the result to be "Just t1", why not
just have "eval1 (If t1 t2 t3) = Just t1", with no case or where
statement?

>
>
> On Mon, Oct 17, 2011 at 4:10 PM, Ivan Lazar Miljenovic
> <ivan.miljenovic at gmail.com> wrote:
>>
>> On 18 October 2011 09:08, kolli kolli <nammukolli04 at gmail.com> wrote:
>> > actual error message is
>> >
>> > homework2.lhs:137:20: parse error on input `where'
>> >
>> > data Term = Tru
>> >           | Fls
>> >           | If Term Term Term
>> >           | Zero
>> >           | Succ Term
>> >           | Pred Term
>> >           | IsZero Term
>> >           deriving Eq
>> >
>>
>> As I said, the error is from your incorrect usage of the case
>> statement; it _should_ look something like:
>>
>> case foo of
>>    bar -> baz
>>    bar' -> baz'
>>
>> >
>> >
>> >
>> >
>> > On Mon, Oct 17, 2011 at 4:03 PM, Ivan Lazar Miljenovic
>> > <ivan.miljenovic at gmail.com> wrote:
>> >>
>> >> On 18 October 2011 08:56, kolli kolli <nammukolli04 at gmail.com> wrote:
>> >> > after parsing a string i am evaluating it...
>> >> > string if t1 then t2 else t3
>> >> > my code is
>> >> > eval1 :: Term ->  Maybe Term
>> >> > eval1(If Tru t2 t3) = Just t2
>> >> > eval1(If Fls t2 t3) = Just t3
>> >> > eval1(If t1 t2 t3) =  case eval t1
>> >> >                     where eval1(If t1 t2 t3) =  Just t1
>> >> >
>> >> > eval :: Term -> Term
>> >> > eval (IsZero Zero) = Tru
>> >> > eval (Zero) = Zero
>> >> > eval(Pred Zero) = Pred Zero
>> >>
>> >> Your case statement is incomplete for starters...
>> >>
>> >> Can you please provide the actual error message as well?  Your
>> >> definition of Term would also be useful.
>> >>
>> >> >
>> >> > On Mon, Oct 17, 2011 at 3:46 PM, Ivan Lazar Miljenovic
>> >> > <ivan.miljenovic at gmail.com> wrote:
>> >> >>
>> >> >> On 18 October 2011 08:43, kolli kolli <nammukolli04 at gmail.com>
>> >> >> wrote:
>> >> >> > hey can anyone tell me what is parser error in parser??Plz help me
>> >> >> > out
>> >> >>
>> >> >> It's when the parser can't parse what it's provided.... providing
>> >> >> the
>> >> >> code that caused the problem and the actual error message is
>> >> >> required
>> >> >> for a more detailed explanation.
>> >> >>
>> >> >> --
>> >> >> Ivan Lazar Miljenovic
>> >> >> Ivan.Miljenovic at gmail.com
>> >> >> IvanMiljenovic.wordpress.com
>> >> >
>> >> >
>> >>
>> >>
>> >>
>> >> --
>> >> Ivan Lazar Miljenovic
>> >> Ivan.Miljenovic at gmail.com
>> >> IvanMiljenovic.wordpress.com
>> >
>> >
>>
>>
>>
>> --
>> Ivan Lazar Miljenovic
>> Ivan.Miljenovic at gmail.com
>> IvanMiljenovic.wordpress.com
>
>



-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
IvanMiljenovic.wordpress.com