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Improve error messages about variance and cardinality preservation #2774

Merged
merged 4 commits into from
Sep 20, 2022
Merged

Improve error messages about variance and cardinality preservation #2774

merged 4 commits into from
Sep 20, 2022

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RustanLeino
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  • Fixes hint to suggest both - and ! instead of just ! when a type parameter is used in a negative position
  • Improves an error message by removing the words "strict positivity", which are confusing and not necessary (see also http://leino.science/papers/krml280.html)

Fixes #2659

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

@RustanLeino RustanLeino marked this pull request as ready for review September 20, 2022 21:04
@RustanLeino RustanLeino enabled auto-merge (squash) September 20, 2022 21:05
@RustanLeino RustanLeino merged commit 21dfe47 into dafny-lang:master Sep 20, 2022
@RustanLeino RustanLeino deleted the issue-2659 branch September 20, 2022 22:06
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@davidcok davidcok davidcok approved these changes

@cpitclaudel cpitclaudel Awaiting requested review from cpitclaudel

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Successfully merging this pull request may close these issues.

Dafny suggests making a type parameter invariant instead of contravariant
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@RustanLeino @davidcok