Opaque constants #1453
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Opaque constants #1453
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Whoops, I rebased those commits in the wrong order. I'll fix that in a rebase after #1423 lands. |
brianhuffman
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Sep 8, 2021
These are just `Constant` terms that have no definition. They are similar to `ExtCns`, except that they are not subject to substitution. As a consequence, opaque constants are allowed to appear in the definition of other constants without being abstracted over. Opauqe constants never reduce, and must be treated as unintepreted in proofs.
`primitive` declarations from Cryptol into `Parameter` declarations in Coq. In the Coq generator, distinguish between `ExtCns` values and opauqe constants. ExtCns values are translated using the Coq `Variable` declaration, wherease opaque constants are translated using the `Parameter` declaration. At top-level, these declarations are essentially the same. However `Parameter` interacts with the module system, whereas `Variable` interacts with the section mechanism. Currently, we make use of neither, but the distinction may eventually be useful.
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This PR adds a notion of "opaque constant" to saw-core. These are
Constantnodes that have no definition. They are similar in many ways toExtCns, but are explicitly not subject to substitution.In particular, opaque constants are allowed to appear in the definition of other constants, whereas
ExtCnsare not (CF discussion on #1430).In
cryptol-saw-core, if aprimitivedeclaration appears in a Cryptol module that is not one of the well-known primitives from the built-in modules we support, it is translated into an opaque constant. Insaw-core-coq, opaque constants are translated into CoqParameterdeclarations. The end result is that we can posit and reason about abstract Cryptol functions in Coq.Note, this is based on #1423, only the final two commits properly belong to this PR.