Tool Support for Correctness-by-Construction

Correctness-by-Construction (CbC) is an approach to incrementally create formally correct programs guided by pre- and postcondition specifications. A program is created using refinement rules that guarantee the resulting implementation is correct with respect to the specification. Although CbC is supposed to lead to code with a low defect rate, it is not prevalent, especially because appropriate tool support is missing. To promote CbC, we provide tool support for CbC-based program development. We present CorC, a graphical and textual IDE to create programs in a simple while-language following the CbC approach. Starting with a specification, our open source tool supports CbC developers in refining a program by a sequence of refinement steps and in verifying the correctness of these refinement steps using the theorem prover KeY. We evaluated the tool with a set of standard examples on CbC where we reveal errors in the provided specification. The evaluation shows that our tool reduces the verification time in comparison to post-hoc verification.