A rule-based language for programming software updates

We describe the design of a rule-based language for expressing changes to Haskell programs in a systematic and reliable way. The update language essentially offers update commands for all constructs of the object language (a subset of Haskell). The update language can be translated into a core calculus consisting of a small set of basic updates and update combinators. The key construct of the core calculus is a scope update mechanism that allows (and enforces) update specifications for the definition of a symbol together with all of its uses. The type of an update program is given by the possible type changes it can cause for an object programs. We have developed a typechange inference system to automatically infer type changes for updates. Updates for which a type change can be successfully inferred and that satisfy an additional structural condition can be shown to preserve type correctness of object programs. In this paper we define the Haskell Update Language HULA and give a translation into the core update calculus. We illustrate HULA and its translation into the core calculus by several examples.