On Sat, 5 Apr 2003 06:55:28 +0100
Glynn Clements
Read-only or write-only attributes could be implemented by throwing an error for prohibited operations. Read-only attributes could be implemented by simply ignoring write operations.
From now on, I propose to tag messages about state handling with the [State] keyword, and invite people who are interested in other aspects of the CGA to start their own discussions.
We could distinguish between two kind of read-only attributes: those which are fixed at creation-time and those which are written somewhere and read somewhere else. Apart from this detail, wich is perhaps unuseful, I think that we should avoid run-time errors when we can model them in the type system, as it leads to a more detailed machine-checked specification. For the specific case, I like an approach where a state variable has two components: a read-only one and a write-only one, as in Variable a = Variable { writeable :: Writeable a, readable :: Readable a } A read-only attribute is exposed with just the "Readable a" type, not with the "Variable a" one. I have to read the other e-mails, and to fit this approach in the getter/setter one, comments are welcome. Vincenzo