Question: WP: `BadPrecondition` "can only happen in traceExecution"

[ocramz]

I'm struggling to understand the remark made in the documentation (under BadPrecondition : https://github.com/LeventErkok/sbv/blob/master/Data/SBV/Tools/WeakestPreconditions.hs#L135), since within wpProveWith we clearly have a precondition check ( https://github.com/LeventErkok/sbv/blob/master/Data/SBV/Tools/WeakestPreconditions.hs#L221) .

Is there a way to emit a BadPrecondition instead?

[LeventErkok]

Note the line:

               constrain $ sNot $ precondition start .=> sAnd (map fst vcs)

simply constrains the proof to all starting states that satisfy the precondition. If your precondition is badly formulated (for instance, if it is const sFalse), then it'll be the same as constrain sFalse; i.e., all proofs will trivially pass. (It's equivalent to proving sFalse .=> anything. (In other words, the state space is empty.)

When you do a traceExecution we'll explicitly check that the concrete state you provide satisfies the precondition, and then we can warn the user if that's not the case. (In other words, you've given a starting state that's not valid.)

[ocramz]

Thank you! Now it makes a lot of sense. I hadn't investigated the mechanics of the Query monad.

[LeventErkok]

This has nothing to do with queries. I’m not sure if I understand your comment.

[ocramz]

apologies, I meant SymbolicT . Mixed up