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GHC 9.14 adds visible forall to GADTs via RequiredTypeArguments

serokell.io 6 hours ago 21 min read ↗ Original

Serokell's report on Dependent Haskell details visible forall in GADTs, namespace-specified imports, and type instances in kind checking.

WHY IT MATTERS

This implementation of visible forall in GADTs is a step toward Dependent Haskell, with the type argument erased and not pattern-matchable. The refactoring of constructor patterns and Core representation prepares GHC for more advanced quantifiers. Engineers can use the new syntax in GHC 9.14.

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The three things worth knowing

Visible forall in GADTs is implemented starting with GHC 9.14 via the RequiredTypeArguments extension.

The report also covers namespace-specified imports and type instances in kind checking.

Constructor patterns were refactored to a mixed-list representation, improving error messages and enabling new syntax.

THE CLUSTER

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