René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Higher-Kinded TypeVars","articleBody":"aka type constructors, generic TypeVars\r\n\r\nHas there already been discussion about those?\r\nI do a lot of FP that results in impossible situations because of this. Consider an example:\r\n\r\n```python\r\nA = TypeVar('A')\r\nB = TypeVar('B')\r\nF = TypeVar('F')\r\n\r\nclass M(Generic[F[X], A]):\r\n    def x(fa: F[A], f: Callable[[A], B]) -\u003e F[B]:\r\n        return map(f, fa)\r\n\r\nM().x([1], str)\r\n```\r\n\r\nI haven't found a way to make this work, does anyone know a trick or is it impossible?\r\nIf not, consider the syntax as a proposal.\r\nReference implementations would be Haskell, Scala.\r\noptimally, the HK's type param would be indexable as well, allowing for `F[X[X, X], X[X]]`\r\n\r\n----\r\n\r\nSummary of current status (by @smheidrich, 2024-02-08):\r\n\r\n- @JelleZijlstra [has indicated interest](https://github.com/python/typing/issues/548#issuecomment-1193345123) in sponsoring a PEP, conditional on a prototype implementation in a major type checker and a well-specified draft PEP.\r\n- Drafting the PEP takes place in @nekitdev's [fork](https://github.com/nekitdev/peps) of the `peps` repo. The [**stub PEP draft**](https://github.com/nekitdev/peps/blob/main/pep-9999.rst) so far contains a few examples of the proposed syntax.\r\n- That same repo's [**GitHub Discussions forum**](https://github.com/nekitdev/peps/discussions) forum has been [designated](https://github.com/python/typing/issues/548#issuecomment-1193348994) as the place to discuss the PEP (and presumably the prototype implementation?). Some limited further discussions have taken place there.\r\n  - If you want to be notified of new discussion threads, I think you have to set the whole repo as \"watched\" in GitHub?\r\n","author":{"url":"https://github.com/tek","@type":"Person","name":"tek"},"datePublished":"2018-03-30T22:56:19.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":222},"url":"https://github.com/548/typing/issues/548"}