No instance for (Monad (FormInput (HandlerT App IO)))

Question

My issue is:

No instance for (Monad (FormInput (HandlerT App IO)))

is such code:

postTest :: Handler Value
postTest = requireAuthId 
           >>= \ pId -> runInputPost $ (,) <$> ireq intField "a" 
                                           <*> ireq intField "b" 
           >>= \ (a, b) -> return $ toJSON $ object []

How can I solve this issue? How will the instance look like?

Answer 1

Looks like a syntax issue to me, I think you just need to wrap runInputPost..."b" inside parentheses. But is there a reason you're not using do-notation for this? I'd find it more natural, and less likely to lead to these syntax errors.