[Haskell-beginners] case in monadic function

[Kovacs David]

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?

Regards, David