[Haskell-beginners] case in monadic function

Thomas Davie tom.davie at gmail.com
Fri Jan 23 09:52:12 EST 2009

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.


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