questionasker.hs

module Parser where
import           Control.Applicative
import           Data.Text

-- the shape of the problem
--
-- we want a list of Parsers, all of different types.
-- we will apply each of them, one after another,
-- in the context of asking questions in some monadic
-- context.

type QParser a = (Text, Parser a)
type Parser a = Text -> Maybe a

parse :: Parser a -> Text -> Maybe a
parse = undefined

collectAll2 :: Monad m
            => (Text -> m Text)
            -> QParser a -> QParser b
            -> m (Maybe (a,b))
collectAll2 ask (q1,p1) (q2,p2) =
  (liftA2 (,))
       <$> (parse p1 <$> ask q1)
       <*> (parse p2 <$> ask q2)

collectAll3 :: Monad m
            => (Text -> m Text)
            -> QParser a -> QParser b -> QParser c
            -> m (Maybe (a,b,c))
collectAll3 ask (q1,p1) (q2,p2) (q3,p3) =
  liftA3 (,,)
     <$> (parse p1 <$> ask q1)
     <*> (parse p2 <$> ask q2)
     <*> (parse p3 <$> ask q3)

-- liftA4 doesn't exist :(
-- collectAll4 :: Monad m
--             => (Text -> m Text)
--             -> QParser a -> QParser b -> QParser c -> QParser d
--             -> m (Maybe (a,b,c,d))
-- collectAll4 ask (q1,p1) (q2,p2) (q3,p3) (q4,p4) =
--   liftA4 (,,,)
--   <*> (parse p1 <$> ask q1)
--   <*> (parse p2 <$> ask q2)
--   <*> (parse p3 <$> ask q3)
--   <*> (parse p4 <$> ask q4)