I found it very difficult to develop a coherent way of representing numeric property values when I was looking at the property values expression evaluator. My initial approach had a structure that looked something like:

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PropertyValue | v Numeric / | \ / v \ Number Length Percentage with inheritance flowing down. The problem was that Numeric types are changeable. Any numeric with a unit power of zero is a number; any numeric with a unit power of one is a measure of some kind, and other unit powers represent intermediate calulation results in the expression evaluator. A PropertyValue can start life as a Length, become a number (unit power 0) through a multop, and then theoretically mutate into a completely different form of measurement, e.g. an Angle. The table I used for this is: * Operations defined on combinations of the types (where a percentage * is treated in the same manner as a number) are: * number anyop number = number * baseunit anyop baseunit2 = Illegal * number multop baseunit = baseunit * number addop baseunit = Illegal * baseunit multop baseunit = baseunit (with changed power) * baseunit^n addop baseunit^n = baseunit^n * baseunit^n addop baseunit^m = Illegal * I don't know how kosher this is, and would appreciate any comments. I am also puzzled by the constraint in the spec (5.9.6 Absolute Numerics) that: In addition, only the mod, addition, and subtraction operators require that the numerics on either side of the operation be absolute numerics of the same unit power. For other operations, the unit powers may be different and the result should be mathematically consistent as with the handling of powers in algebra. As I read this, it means that, while I can divide a <length> by a number, resulting in a <length> of the same unit power, I cannot take the mod of a <length> using a number. Can anyone explaing the reasons for this restriction? The approach taken in the current expression evaluator is that all arithmetic operations involving property values require that the operand be another property value, and the operation generates a new property value object. This may well be the cleanest way, but I am experimenting with expressing the result of the operation directly in the PropertyValue object on which the arithmetic operation is invoked. In order for this to work, I had to eliminate the subclasses of Numeric. These (Length, Percentage, IntegerType, Angle, Time, Frequency and possibly Number) remain as "static" classes which provide the class methods makeLength, makePercentage, etc, all of which return Numerics. The type of a Numeric is distinguished by the baseunit, which may change as a result of arithmetic operations. I am currently working my way through the Numeric and other subclasses of PropertyValue, and setting up any necessary PropertyValue objects to express the initial values of the properties in Properties.java, the monster properties file. The propertyStacks in PropertyConsts.java will contain PropertyTriplet objects, which potentially contain specified, computed and actual property values. Specified is a String; the othes are PropertyValue objects. I will upload the latest versions to my web page later tonight, for anyone who is interested. Peter --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, email: [EMAIL PROTECTED]