Task: Parsing_RPN calculator algorithm







Python: def op_pow(stack):
    b = stack.pop(); a = stack.pop()
    stack.append( a ** b )
def op_mul(stack):
    b = stack.pop(); a = stack.pop()
    stack.append( a * b )
def op_div(stack):
    b = stack.pop(); a = stack.pop()
    stack.append( a / b )
def op_add(stack):
    b = stack.pop(); a = stack.pop()
    stack.append( a + b )
def op_sub(stack):
    b = stack.pop(); a = stack.pop()
    stack.append( a - b )
def op_num(stack, num):
    stack.append( num )
    
ops = {
 '^': op_pow,
 '*': op_mul,
 '/': op_div,
 '+': op_add,
 '-': op_sub,
 }

def get_input(inp = None):
    'Inputs an expression and returns list of tokens'
    
    if inp is None:
        inp = input('expression: ')
    tokens = inp.strip().split()
    return tokens

def rpn_calc(tokens):
    stack = []
    table = ['TOKEN,ACTION,STACK'.split(',')]
    for token in tokens:
        if token in ops:
            action = 'Apply op to top of stack'
            ops[token](stack)
            table.append( (token, action, ' '.join(str(s) for s in stack)) )
        else:
            action = 'Push num onto top of stack'
            op_num(stack, eval(token))
            table.append( (token, action, ' '.join(str(s) for s in stack)) )
    return table

if __name__ == '__main__':
    rpn = '3 4 2 * 1 5 - 2 3 ^ ^ / +'
    print( 'For RPN expression: %r\n' % rpn )
    rp = rpn_calc(get_input(rpn))
    maxcolwidths = [max(len(y) for y in x) for x in zip(*rp)]
    row = rp[0]
    print( ' '.join('{cell:^{width}}'.format(width=width, cell=cell) for (width, cell) in zip(maxcolwidths, row)))
    for row in rp[1:]:
        print( ' '.join('{cell:<{width}}'.format(width=width, cell=cell) for (width, cell) in zip(maxcolwidths, row)))

    print('\n The final output value is: %r' % rp[-1][2])





Ada: with Ada.Text_IO, Ada.Containers.Vectors;

procedure RPN_Calculator is

  package IIO is new Ada.Text_IO.Float_IO(Float);

   package Float_Vec is new Ada.Containers.Vectors
     (Index_Type => Positive, Element_Type => Float);
   Stack: Float_Vec.Vector;

   Input: String := Ada.Text_IO.Get_Line;
   Cursor: Positive := Input'First;
   New_Cursor: Positive;

begin
   loop
      
      while Cursor <= Input'Last and then Input(Cursor)=' ' loop
         Cursor := Cursor + 1;
      end loop;

      exit when Cursor > Input'Last;

      New_Cursor := Cursor;
      while New_Cursor <= Input'Last and then Input(New_Cursor) /= ' ' loop
         New_Cursor := New_Cursor + 1;
      end loop;

      
      declare
         Last: Positive;
         Value: Float;
         X, Y: Float;
      begin
         IIO.Get(From => Input(Cursor .. New_Cursor - 1),
                 Item => Value,
                 Last => Last);
         Stack.Append(Value);
         Cursor := New_Cursor;

      exception 
         when others =>
            Y := Stack.Last_Element; Stack.Delete_Last; 
            X := Stack.Last_Element; Stack.Delete_Last; 
            case Input(Cursor) is
               when '+' => Stack.Append(X+Y);
               when '-' => Stack.Append(X-Y);
               when '*' => Stack.Append(X*Y);
               when '/' => Stack.Append(X/Y);
               when '^' => Stack.Append(X ** Integer(Float'Rounding(Y)));
               when others => raise Program_Error with "unecpected token '"
                  & Input(Cursor) & "' at column" & Integer'Image(Cursor);
            end case;
            Cursor := New_Cursor;
      end;

      for I in Stack.First_Index .. Stack.Last_Index loop
         Ada.Text_IO.Put(" ");
         IIO.Put(Stack.Element(I), Aft => 5, Exp => 0);
      end loop;
      Ada.Text_IO.New_Line;
   end loop;

   Ada.Text_IO.Put("Result = ");
   IIO.Put(Item => Stack.Last_Element, Aft => 5, Exp => 0);


end RPN_Calculator;