with simple_i, stacks;
use simple_i, stacks;

procedure post2 is

end_of_exp : boolean := false;
st : Stack;
next, val : character;

function ISP(x : in character) return integer is
begin
   case x is
      when '^' => return(4);
      when '*' | '/' => return(3);
      when '+' | '-' => return(1);
      when '(' => return(0);
      when '.' => return(-1);
      when others => null;
   end case;
end ISP;

function ICP(y : in character) return integer is
begin
   case y is 
      when '^' => return(4);
      when '*' | '/' => return(3);
      when '+' | '-' => return(1);
      when '(' => return(5);
      when others => null;
   end case;
end ICP;

begin
   Push ('.', st);
   put("Please input the infix expression > ");

   while (not end_of_exp) loop
      get(next);
      case next is
         when '.' => while (not Empty(st)) loop
                        put(Top(st));
                        Pop(st);
                     end loop;
                     end_of_exp := true;
         when '1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'|'0' => put(next);
         when ')' => while (Top(st) /= '(') loop
                        put(Top(st));
                        Pop(st);
                     end loop;
                     Pop(st);
         when others => while (ISP(Top(st)) >= ICP(next)) loop
                           put(Top(st));
                           Pop(st);
                        end loop;
                        Push(next, st);
      end case;
   end loop;
end post2;