K. Rustan M. Leino RiSE, Microsoft Research 17 July 2009 JML seminar Dagstuhl, Germany

experimental language sequential, object based (no subclassing) specifications in the style of dynamic frames coarse-grained frames (at the level of whole objects, not individual memory locations)

queue linked list with head/tail pointers in-situ list reversal integer set binary tree Schorr-Waite marking algorithm

Program ::= Class* Class ::= class C { Member* } Member ::= Field Method Function

A frame is a set of locations A dynamic frame (in the sense of Dafny) is an expression that denotes a frame Methods have modifies clauses Functions have reads clauses

Dynamic-frame specifications are useful and flexible A language design around dynamic frames can be simple Thus good in teaching? Specifications are verbose, but perhaps simplification techniques can be applied (like in Spec# or Chalice) Currently missing in Dafny: scopes for axioms

Pure methods are hard, functions are easy SMT solvers work better with ghost fields than with functions Reachability is not always necessary in specifications Sets and sequences are nice as value types Generics are a cinch Decreases bound checks can be more liberal than naïve translation

SMT solvers can be used for functional- correctness verification Inductive predicates seem useful cases fit nicely with matching triggers take us in the direction of the input languages of interactive theorem provers Need: better views/visualizations of program states to clarify error messages and, generally, what’s going on

Dafny is available as open source: