[Haskell-beginners] StateT, list monad

[Michael Mossey]

Trying to understand Douglas Auclair's article
"MonadPlus - What a super monad!" here
<http://www.haskell.org/sitewiki/images/6/6a/TMR-Issue11.pdf>

Defines

splits :: Eq a => [a] -> [(a,[a])]
splits list = do x <- list
                 return (x, delete x list)

choose :: Eq a => StateT [a] [] a
choose = StateT (\s -> splits s)

I'm trying to understand what "StateT [a] [] a" means:

I wrote

t1 :: StateT [Int] [] [Int]
t1 = do
  s <- get
  return s

That compiles. Then I tried to write

t2 :: StateT [Int] [] [Int]
t2 = do
  x <- [1,2,3]
  s <- get
  return (x:s)

I thought this would be fine because [1,2,3] is an example of a list monad.

But I get

"Can't match expected type StateT [Int] [] t
against inferred type [a]"