stepleft.hs

-- Given [a,b] - Gives [a,b,a,b]
wutDecoder :: Monad f => Decoder f [Int]
wutDecoder = withCursor $ \curs -> do
  -- Move into the array
  x <- down curs
  -- Decode first
  a <- int pint x
  -- Step to the right
  x' <- moveRightN 1 x
  -- Decode that one
  b <- int pint x'
  -- Jump to the left
  x'' <- moveLeft1 x'
  -- Decode that one again
  c <- int pint x''
  -- Step back to the right again
  x''' <- moveRightN 1 x''
  -- Decode that one
  d <- int pint x'''
  -- Shake it all out
  pure [a,b,c,d]

-- Given [a,b,c] -- Gives [a,c,b,c,a]
fooDecoder :: Monad f => Decoder f [Int]
fooDecoder = withCursor $ \curs -> do
  -- Move into array
  x <- down curs
  -- Decode '1'
  a <- int pint x
  -- Step right twice
  x' <- moveRightN 2 x
  -- Decode '3'
  b <- int pint x'
  -- Step left once
  x'' <- moveLeftN 1 x'
  -- Decode '2'
  c <- int pint x''
  -- Step right once
  x''' <- moveRightN 1 x''
  -- Decode '3'
  d <- int pint x'''
  -- Step left twice
  x'''' <- moveLeftN 2 x'''
  -- Decode '1'
  e <- int pint x''''
  -- Expecting [1,3,2,3,1]
  pure [a,b,c,d,e]