Type-Safe Update Programming

Many software maintenance problems are caused by using text editors to change programs. A more systematic and reliable way of performing program updates is to express changes with an update language. In particular, updates should preserve the syntaxand typecorrectness of the transformed object programs. We describe an update calculus that can be used to update lambdacalculus programs. We develop a type system for the update language that infers the possible type changes that can be caused by an update program. We demonstrate that type-safe update programs that fulfill certain structural constraints preserve the type-correctness of lambda terms.