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 On Mon, Oct 17, 2011 at 4:03 PM, Ivan Lazar Miljenovic < ivan.miljenovic@gmail.com> wrote:

On 18 October 2011 08:56, kolli kolli 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 wrote:

...

On 18 October 2011 08:43, kolli kolli 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@gmail.com IvanMiljenovic.wordpress.com

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