1/1: Building lets (lets.idr)
Error: While processing right hand side of dolet2. When unifying:
    Maybe Int
and:
    Maybe String
Mismatch between: Int and String.

lets:22:39--22:40
 18 |          pure (x' + y')
 19 | 
 20 | dolet2 : Maybe Int -> Maybe Int -> Maybe Int
 21 | dolet2 x y
 22 |     = do let Just x' : Maybe String = x
                                            ^