StateTを使ってより簡潔に?

import Control.Monad.State

ten = [0..9]

getNum :: StateT [Int] [] Int
getNum = StateT $ ?ns -> do{n <- ns; return (n, filter (n/=) ns)}

sendmory = do
  s <- getNum
  if s==0 then lift [] else return ()
  m <- getNum
  if m==0 then lift [] else return ()
  e <- getNum
  n <- getNum
  d <- getNum
  o <- getNum
  r <- getNum
  y <- getNum
  if s*1000+e*100+n*10+d+m*1000+o*100+r*10+e==m*10000+o*1000+n*100+e*10+y then return (s,e,n,d,m,o,r,y) else lift []

instance (Show s, Show e, Show n, Show d, Show m, Show o, Show r, Show y)=>
  Show (s,e,n,d,m,o,r,y) where
  show (s,e,n,d,m,o,r,y) = "("++show s++","++show e++","++show n++","++show d++","++show m++","++show o++","++show r++","++show y++")"
  
main = print (evalStateT sendmory ten)

簡潔になった。しかし、いきなり StateT s [] a とか言われても「は？」という感じは否めない。