Conditional logics are logics which augment traditional logical implication with modal operators corresponding to other notions of condition (for example, the causal conditional $A\; \square\!\!\!\!\to B$ reads "$A$ causes "B", or probabilistic conditioning "$A|B$", which reads "$A$ given $B$").
Typically these logics are studied model-theoretically, but I've wondered about their applications to programming language design (for example, to type imperative actions).
I'd appreciate references to their proof theory (ie, sequent calculus/natural deduction), or to programming languages with types based on these kinds of modal operators.
Thanks!
EDIT: The Stanford Encyclopedia of Philosophy has a nice introduction to the subject.