Use a typeclass for non informative types #27
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Leveraging the new call_subtac primitive to call the typeclass resolution tactic and obtain a well-typed dictionary.
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This removes the built-in knowledge of non-informative types that is present in the checker, and instead encodes this property via a typeclass. When the checker needs to construct a "non_informative_witness" for a type, essentially a revealing function, instead of applying some built-in rules it can now just call the typeclass resolution tactic, via the new
call_subtacprimitive (FStarLang/FStar#3226), obtaining both the dictionary for the constraint and a proof of its well-typing.All examples work as before (and importantly #11 still works, since the resolution tactic does not need to re-check its goal). Also a big chunk of checker about derivations of non_informative constraints is now gone: we basically get the derivation for free from the
call_subtacinvocation.The main advantage is that non-informative types are now open, and any user can add a type to the class.