{-# LANGUAGE TypeFamilies #-}

module Control.Monad.Trans.Interruptible where

import Control.Monad.Trans.Interruptible.Class

{- |
Folds the second list with the function applied to the first,
intercalating the evaluation. That is:

@
intercalateM f [a00, a10, a20] [b1, b2] = do
  a01 <- f a00 b1
  a11 <- f a10 b1
  a21 <- f a20 b1
  a02 <- f a11 b2
  a12 <- f a21 b2
  a22 <- f a31 b2
  return [a02, a12, a22]
@

Usefull for consuming lazy sequences.
-}
intercalateM :: (InterruptibleMonadTrans m, Monad n) => (b -> a -> m n a) -> [b] -> [RDt m a] -> n [RDt m a]
intercalateM _ [] aa = return aa
intercalateM f (b:bb) aa = do
  aa' <- mapM (\x -> runT x $ f b) aa
  intercalateM f bb aa'