Static contract checking for Haskell

• Static Contract checking for Haskell, Dana Xu, Simon Peyton Jones, and Koen Claessen. Submitted to POPL'09.
  • A4 postscript

  Abstract. Program errors are hard to detect and are costly both to programmers who spend significant efforts in debugging, and for systems that are guarded by runtime checks. Static verification techniques have been applied to imperative and object-oriented languages, like Java and C#, but few have been applied to a higher-order lazy functional language, like Haskell. In this paper, we describe a sound and automatic static verification tool for Haskell, that is based on contracts and symbolic execution. Our approach is modular and gives precise blame assignments at compile-time in the presence of higher-order functions and laziness.

• Slides (PDF) of a talk given at the Midlands Graduate School Christmas Lectures, 2007.

• Extended static checking for Haskell, Dana Xu, Haskell Workshop 2006.
  • [A4 Postscript]

  Abstract. Program errors are hard to detect and are costly both to programmers who spend significant efforts in debugging, and to systems that are guarded by runtime checks. Extended static checking can reduce these costs by helping to detect bugs at compile-time, where possible. Extended static checking has been applied to object-oriented languages, like Java and C#, but it has not been applied to a lazy functional language, like Haskell. In this paper, we describe an extended static checking tool for Haskell, named ESC/Haskell, that is based on symbolic computation and assisted by a few novel strategies. One novelty is our use of Haskell as the specification language itself for pre/post conditions. Any Haskell function (including recursive and higher order functions) can be used in our specification which allows sophisticated properties to be expressed. To perform automatic verification, we rely on a novel technique based on symbolic computation that is augmented by counter-example guided unrolling. This technique can automate our verification process and be efficiently implemented.