INTERFACE USENIX BRAND "v1";

EXCEPTION ZeroDivisor;

TYPE Calculator = OBJECT COLLECTIBLE
  METHODS

    Clear (),
    CurrentValue () : REAL,

    Add (value : REAL),
    Subtract (value : REAL),
    Multiply (value : REAL),
    Divide (value : REAL) RAISES ZeroDivisor END

  END;

TYPE Factory = OBJECT
  METHODS
    NewCalculator () : Calculator
  END;

EXCEPTION NoValueInMemory;

TYPE MemCalculator = OBJECT COLLECTIBLE SUPERTYPES Calculator END
  METHODS
    MemSet (value : REAL),
    MemGet () : REAL RAISES NoValueInMemory END,

    MemAdd () RAISES NoValueInMemory END,
    MemSubtract () RAISES NoValueInMemory END,
    MemMultiply () RAISES NoValueInMemory END,
    MemDivide () RAISES ZeroDivisor, NoValueInMemory END
  END;

TYPE OpType = ENUMERATION Clear,
     Add, Subtract, Multiply, Divide,
     MemSet, MemAdd, MemSubtract, MemMultiply, MemDivide END;

TYPE PossibleValue = OPTIONAL REAL;

TYPE Operation = RECORD
  kind : OpType,
  val : PossibleValue
END;

TYPE CalcTape = SEQUENCE OF Operation;

TYPE MemCalculatorWithTape = OBJECT COLLECTIBLE SUPERTYPES MemCalculator END
  METHODS
    GetTape () : CalcTape
  END;

.