| Abstract / Kurzbeschreibung: |
For a number of programming languages, among them Eiffel, C, Java, and Ruby, Hoare-style logics
and dynamic logics have been developed. In these logics, pre- and postconditions are typically formulated
using potentially effectful programs. In order to ensure that these pre- and postconditions behave like logical
formulae (that is, enjoy some kind of referential transparency), a notion of purity is needed. Here, we introduce a
generic framework for reasoning about purity and effects. Effects are modelled abstractly and axiomatically, using
Moggi’s idea of encapsulation of effects as monads.We introduce a dynamic logic (from which, as usual, a Hoare
logic can be derived) whose logical formulae are pure programs in a strong sense. We formulate a set of proof
rules for this logic, and prove it to be complete with respect to a categorical semantics. Using dynamic logic, we
then develop a relaxed notion of purity which allows for observationally neutral effects such writing on newly
allocated memory. |
