<div dir="ltr"><div>I didn't say anything when you were requesting use cases, so I have no right to complain, but I'm still a little disappointed that this doesn't fix my (admittedly very minor) issue: <a href="https://www.reddit.com/r/haskell/comments/3am0qa/existentials_and_the_heterogenous_list_fallacy/csdwlp2/?context=8&depth=9">https://www.reddit.com/r/haskell/comments/3am0qa/existentials_and_the_heterogenous_list_fallacy/csdwlp2/?context=8&depth=9</a></div><div><br></div><div>For those who don't want to click on the reddit link: I would like to be able to write something like<code> map show ([1, 'a', "b"] :: [forall a. Show a => a])<span style="font-family:arial,sans-serif">, and have it work.<br></span></code></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Sep 4, 2019 at 8:13 AM Alejandro Serrano Mena <<a href="mailto:trupill@gmail.com">trupill@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Hi all,</div><div>As I mentioned some time ago, we have been busy working on a new implementation of `ImpredicativeTypes` for GHC. I am very thankful to everybody who back then sent us examples of impredicativity which would be nice to support, as far as we know this branch supports all of them! :)</div><div><br></div><div>If you want to try it, at <a href="https://gitlab.haskell.org/trupill/ghc/commit/a3f95a0fe0f647702fd7225fa719a8062a4cc0a5/pipelines?ref=quick-look-build" target="_blank">https://gitlab.haskell.org/trupill/ghc/commit/a3f95a0fe0f647702fd7225fa719a8062a4cc0a5/pipelines?ref=quick-look-build</a> you can find the result of the pipeline, which includes builds for several platforms (click on the "Artifacts" button, the one which looks like a cloud, to get them). The code is being developed at <a href="https://gitlab.haskell.org/trupill/ghc" target="_blank">https://gitlab.haskell.org/trupill/ghc</a>.</div><div><br></div><div>Any code should run *unchanged* except for some eta-expansion required for some specific usage patterns of higher-rank types. Please don't hesitate to ask any questions or clarifications about it. A merge request for tracking this can be found at <a href="https://gitlab.haskell.org/ghc/ghc/merge_requests/1659" target="_blank">https://gitlab.haskell.org/ghc/ghc/merge_requests/1659</a></div><div><br></div><div>Kind regards,</div><div>Alejandro<br></div></div>
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