Exclusive enumeration #1085
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Exclusive enumeration #1085
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@robdockins #973 contains a good suggestion by you about setting the stride. Are you planning to tackle that here as well? |
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I haven't thought about it much since I made that suggestion. Is that something you think people would find useful? |
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Yes, and I didn't want to comment to disappear -- I see this PR is labeled "Fixes #973". Would you be willing to capture your idea in a new issue? |
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CF #1087 |
brianhuffman
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Mar 2, 2021
This allows us to express enumerations with exclusive upper bounds. In contrast with the `Literal` constraint, `LiteralLessThan n a` express that `a` contains all the literals strictly less than `n`, and explicitly allows `n` to be `inf` for unbounded types like `Integer` and `Rational`. It is possible to define `Literal n a` as `(fin n, LiteralLessThan (n+1) a)` instead of leaving it primitve. However, this makes infered types and error messages worse, IMO. As it stands, the typechecker has no real knowledge of the connection between `Literal` and `LiteralLessThan`.
`[ x .. < y ]` --> ``fromToLessThan`{first=x, bound=y}``
`[ x:t .. < y ]` --> ``fromToLessThan`{first=x, bound=y, a=t}``
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…ons. This includes the following submodule PRs: - GaloisInc/cryptol#1085 "exclusive-enumeration" - GaloisInc/saw-core#188 "PLiteralLessThan"
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Add support for enumerations with exclusive upper bounds. This allows us to capture two different boundary conditions: empty sequences and infinite sequences.
As a result, we can redefine
generatein a way that allows LHS indexing to likewise produce infinite and empty sequencesFixes #1063
Fixes #973
There are still some questions we need to answer regarding #1062.