66e5e324
by Vladislav Zavialov at 2026-03-27T04:42:25-04:00
Extend HsExpr with the StarIsType syntax (#26587, #26967)
This patch allows kinds of the form `k -> *` and `* -> k` to occur in
expression syntax, i.e. to be used as required type arguments.
For example:
{-# LANGUAGE RequiredTypeArguments, StarIsType #-}
x1 = f (* -> * -> *)
x2 = f (forall k. k -> *)
x3 = f ((* -> *) -> Constraint)
Summary of the changes:
* Introduce the HsStar constructor of HsExpr and its extension field XStar.
It is analogous to HsStarTy in HsType.
* Refactor HsStarTy to store the unicode flag as TokStar, defined as
type TokStar = EpUniToken "*" "★" -- similar to TokForall, TokRArrow, etc.
The token is stored in the extension field and replaces the Bool field.
* Extend the `infixexp2` nonterminal to parse `*` as a direct argument of `->`.
This is more limited than the full StarIsType syntax, but has the nice
property of not conflicting with the multiplication operator `a * b`.
Test case: T26967 T26967_tyop