[Haskell-beginners] case in monadic function

[Thomas Davie]

On 23 Jan 2009, at 15:40, Kovacs David wrote:

> Hello!
>
> I have a function like this: http://rafb.net/p/8E66FI29.html,  
> starting with evalState. The problem is with checkPredName cause  
> it's return type is SemanticError what's not a monadic value but  
> case waiting for m a (as the error message sais), but if I use  
> return to checkPredName then ofc the pattern match will fail. How  
> can I fix this?

This looks a lot to me like you need to look at the Error e => Either  
e applicative.

Bob