Stateless and pure
Stateless is first a semantic notion, meaning that a stateless feature does not refer to any state. To show that property to the clients, we add a syntactical notation based on the notion of constants in Eiffel, this looks like:
f (a: STRING): SOME_TYPE = do create Result.make (a) ... end
With some validity rules:
- only unqualified calls to stateless features are permitted.
With some validity rules for redefinition:
- once a routine is stateless its redefinitions have to be stateless.
- a stateful routine can become stateless.