functor
import System Space
define
% from CTMCP,  p. 773

fun {Solve Script}
   {SolveStep {Space.new Script} nil} end

fun {SolveStep S SolTail}
   case {Space.ask S}
   of failed then SolTail
   [] succeeded then {Space.merge S}|SolTail
   [] alternatives(N) then {SolveLoop S 1 N SolTail} end end

fun lazy {SolveLoop S I N SolTail}
   if I>N then SolTail
   elseif I==N then
      {Space.commit S I}
      {SolveStep S SolTail}
   else
      C={Space.clone S}
      NewTail={SolveLoop S I+1 N SolTail}
   in
      {Space.commit C I}
      {SolveStep C NewTail} end end

fun {SolveOne F}
   L={Solve F} in
   if L==nil then nil else [L.1] end end

fun {SolveAll F}
   L={Solve F}
   proc {TouchAll L}
      if L==nil then skip else {TouchAll L.2} end end in
   {TouchAll L}
   L end
%Exercise starts here:

fun {Digit}
        choice 0 [] 1 [] 2 [] 3 [] 4 [] 5 [] 6 [] 7 [] 8 [] 9 end
    end
    fun {TwoDigit}
        10*{Digit}+{Digit}
    end
    {System.show {SolveAll TwoDigit}}

end