Towards a EDSL for defining concise models
stevana opened this issue · comments
PR #171 introduces a small language, inspired by Z/Event-B and TLA+, for specifying concise and showable models.
The, perhaps naive, idea that I have is that it will allows us to more easily port examples from Event-B and TLA+ to our setting. I say naive because the settings are obviously very different. They use classical meta-theory where as we have to be more constructive (unless we want to implement a theorem prover), and it shows in that many operations in the PR are partial.
I'd be curious to hear what other people think about this topic!
For N-ary relations/relational algebra it could be helpful to do something like:
Or use ideas from Datafun: https://github.com/rntz/datafun ?
Another idea is to have pre- and post-conditions use a new datatype instead of Bool, which gives better indication of what went wrong. For example:
precondition :: Model -> Action -> Logic
precondition _ (Apa x) = Boolean "x < 5" (x < 5) .&. Boolean "x > 10" (x > 10)
data Logic = Boolean String Bool | Logic .&. Logic
test :: Logic -> Either String ()
test (Boolean str b) | b = Right ()
| otherwise = Left str
test (p .&. q) = do
Right () <- test p
test qWe can then instead of just printing "precondition failed for Apa" show why it failed.
We can also be more fancy and have test accumulate error strings. Or make Boolean take a data Predicate = forall a. (Ord a, Show a) => LessThan a a | ... instead of a String and a Bool, the advantage of this approach apart from not having to provide the string is that we can also negate the predicate, which is helpful when adding disjunction to Logic.