Adding Reasoners(How to extend Rodin Tutorial)
In this part
In this part we will see how to contribute to the sequent prover of Rodin. Rodin support several provers. Some are embedded such as NewPP, or the sequent prover will talk about here, and some are added through plug-ins (as the Atelier B provers : ML, PP, P0, etc). What we will detail here is how to add a new proof rule within the sequent prover of Rodin. The sequent prover provides a set of tactic applying proof rules. These rules are either rewriting rules (see rewriting rules) or inference rules (see inference rules) that helps the user in the interactive proof mode. Moreover, they can be either automatic (auto tactic and/or post tactic) or manual (using providers in the UI that paint their applications in red on formulas).
Principles
Contributing to Rodin sequent prover is done by adding tactics. These tactics apply on proof tree nodes which often involve a set of reasoners. The reasoners apply on the sequent of a given proof tree node. A reasoner is (and has to be) quite "rough" : it shall take the input sequent and calculate a given proof rule that will apply on it (if possible), whereas a tactic could be smarter. In fact, a tactic can involve several reasoners, thus apply them in loops, and combine them.
A reasoner is actually a quite critical piece of code, that one human should understand at first sight, and be convinced about its correctness. If one codes a wrong reasoner, one breaks the whole soundness of proofs done within Rodin! As they are written in pure java, and accorded to the previous considerations, they have to be the simpliest and most readable as possible. Finally, it is needed to write tests that covers all the possible cases of application of one given reasoner (which will not detail here).
