https://gist.github.com/yonta/5851577#file-sendmoremoney2-sml に触発されて書いてみた。力ずくで解く例。

sendmoremoney.sml

(**
 *   SEND
 * + MORE
 * ------
 *  MONEY
 *
 * S,E,N,D,M,O,R,Y
 *
 * run:
 * - Option.app (print o pp) (search ())
 *)
structure L = List

fun toInt xs = L.foldl (fn (x,i)=> x + i * 10) 0 xs

fun pp (xs as [S,E,N,D,M,O,R,Y]) =
  let
    val int = Int.toString
  in
    concat["  ", concat(map int [S,E,N,D]), "\n"
          ,"+ ", concat(map int [M,O,R,E]), "\n"
          ,"------\n"
          ," " , concat(map int [M,O,N,E,Y]), "\n"
          ]
  end
  | pp _ = raise Domain

fun unique [] = true
  | unique (x::xs) = not (L.exists (fn e=>e=x) xs)
             andalso unique xs

fun isSolved (xs as [S,E,N,D,M,O,R,Y]) =
    let
      val send = toInt [S,E,N,D]
      val more = toInt [M,O,R,E]
      val money = toInt [M,O,N,E,Y]
    in
      unique xs
        andalso 0<>S
        andalso 0<>M
        andalso send + more = money
    end
  | isSolved _ = false

fun toList x =
  let
    fun toList' v = if v < 10 then [v]
                    else (v mod 10)::toList' (v div 10)
  in rev (toList' x)
  end

fun extend n xs =
  let
    val len = length xs
  in
    if len < n
    then L.tabulate (n - len, fn _=> 0)@xs
    else xs
  end

fun permutation xs =
  let
    fun next xs = toList ((toInt xs) + 1)
    fun go xs = if unique xs then xs
                else go (next xs)
  in go (next xs)
  end

fun search () =
  let
    fun search' xs =
      if isSolved xs
      then SOME xs
      else search' (permutation xs)
  in
    search' [0]
  end ;