Observability for Pair Pattern Calculi

Abstract

Inspired by the notion of solvability in the λ-calculus, we define a notion of observability for a calculus with pattern matching. We give an intersection type system for such a calculus which is based on non-idempotent types. The typing system is shown to characterize the set of terms having canonical form, which properly contains the set of observable terms, so that typability alone is not sufficient to characterize observability. However, the inhabitation problem associated with our typing system turns out to be decidable, a result which — together with typability — allows to obtain a full characterization of observability.