リストモナドで解く

(追記： http://haskell.g.hatena.ne.jp/nobsun/20061019/alphametic のほうがとてもスマート。)

ten = [0..9]

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

sendmory l0 = do
  (s,l1) <- getNum l0
  if s==0 then [] else return ()
  (m,l2) <- getNum l1
  if m==0 then [] else return ()
  (e,l3) <- getNum l2
  (n,l4) <- getNum l3
  (d,l5) <- getNum l4
  (o,l6) <- getNum l5
  (r,l7) <- getNum l6
  (y,l8) <- getNum l7
  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 []

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 (sendmory ten)

コンパイルすればまずまず速い。

ここで、Stateモナドなパターンが現れているので：