Add support for the variant operator in the type and effect system
#1209
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variant operator in the type and effect system
bugarela
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Oct 17, 2023
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October 20, 2023 15:42
This also requires adding a new constraint `isDefined` that holds iff a type that unifies with the given type is defined in the context.
Allows us to find and transform values from an iterable
- Nullary constructors where being incorrectly defined as lambdas, when they should just be values. - We were not adding the type annotation of the defined type to the operator. But we want this, since in ensures we do not construct open rowed variants and ensures that we have the right topological sorting to ensure the variant constructors are after the defined types.
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Thanks for the review and for catching my oversights. |
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Addresses the first half of #244.
The
variantoperator is the builtin operator introduced in #1206 that injects a value into a sum type. I.e.,type T = A(int) | B; val a : T = variant("A", 42).This PR adds support in the type system for checking and inferring the type of this operator.
The most significant change is the introduction of a new constraint
isDefined(t)which holds when the type schematunifies with a defined type. This is required and foretold by the RFC001, approved in #1062. It ensures that users cannot introduces open-rowed variants, since we have decided that the complexity of allowing open, anonymous variant types is undesirable.This PR also corrects the logic around generating the sum type injector operators introduced in #1206.
Please see the commit messages for context. Review by commit my also be helpful.
CHANGELOG.mdfor any new functionalityREADME.mdupdated for any listed functionality