{"action":"created","issue":{"url":"https://api.github.com/repos/tweag/ghc/issues/243","repository_url":"https://api.github.com/repos/tweag/ghc","labels_url":"https://api.github.com/repos/tweag/ghc/issues/243/labels{/name}","comments_url":"https://api.github.com/repos/tweag/ghc/issues/243/comments","events_url":"https://api.github.com/repos/tweag/ghc/issues/243/events","html_url":"https://github.com/tweag/ghc/issues/243","id":386135668,"node_id":"MDU6SXNzdWUzODYxMzU2Njg=","number":243,"title":"Multiplicity argument of constructors appear in type errors","user":{"login":"aspiwack","id":1413217,"node_id":"MDQ6VXNlcjE0MTMyMTc=","avatar_url":"https://avatars1.githubusercontent.com/u/1413217?v=4","gravatar_id":"","url":"https://api.github.com/users/aspiwack","html_url":"https://github.com/aspiwack","followers_url":"https://api.github.com/users/aspiwack/followers","following_url":"https://api.github.com/users/aspiwack/following{/other_user}","gists_url":"https://api.github.com/users/aspiwack/gists{/gist_id}","starred_url":"https://api.github.com/users/aspiwack/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/aspiwack/subscriptions","organizations_url":"https://api.github.com/users/aspiwack/orgs","repos_url":"https://api.github.com/users/aspiwack/repos","events_url":"https://api.github.com/users/aspiwack/events{/privacy}","received_events_url":"https://api.github.com/users/aspiwack/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":0,"created_at":"2018-11-30T10:49:30Z","updated_at":"2018-12-07T15:20:05Z","closed_at":null,"author_association":"NONE","body":"I don't know if it's systematic or only certain type errors. I spotted it in the test `T12785b`, where we see things like:\r\n\r\n```\r\n        bound by a pattern with constructor:\r\n                   Branch :: forall a (n2 :: Peano).\r\n                             a -->.(n) HTree n2 (HTree ('S n2) a) -->.(n) HTree ('S n2) a,\r\n```\r\n\r\nIn that particular case, it's particularly wrong because it is `Branch`-in-a-pattern, which is _not_ multiplicity polymorphic!\r\n\r\nIt's related to, but probably different than, #239 ."},"comment":{"url":"https://api.github.com/repos/tweag/ghc/issues/comments/445264683","html_url":"https://github.com/tweag/ghc/issues/243#issuecomment-445264683","issue_url":"https://api.github.com/repos/tweag/ghc/issues/243","id":445264683,"node_id":"MDEyOklzc3VlQ29tbWVudDQ0NTI2NDY4Mw==","user":{"login":"monoidal","id":501854,"node_id":"MDQ6VXNlcjUwMTg1NA==","avatar_url":"https://avatars1.githubusercontent.com/u/501854?v=4","gravatar_id":"","url":"https://api.github.com/users/monoidal","html_url":"https://github.com/monoidal","followers_url":"https://api.github.com/users/monoidal/followers","following_url":"https://api.github.com/users/monoidal/following{/other_user}","gists_url":"https://api.github.com/users/monoidal/gists{/gist_id}","starred_url":"https://api.github.com/users/monoidal/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/monoidal/subscriptions","organizations_url":"https://api.github.com/users/monoidal/orgs","repos_url":"https://api.github.com/users/monoidal/repos","events_url":"https://api.github.com/users/monoidal/events{/privacy}","received_events_url":"https://api.github.com/users/monoidal/received_events","type":"User","site_admin":false},"created_at":"2018-12-07T15:20:05Z","updated_at":"2018-12-07T15:20:05Z","author_association":"NONE","body":"After #254, the situation improves a bit but the issue is not yet fixed.\r\n\r\nWe're now getting\r\n```\r\n                   Branch :: forall a (n2 :: Peano).\r\n                             a -> HTree n2 (HTree ('S n2) a) -> HTree ('S n2) a,\r\n```\r\n`n` is renamed to `n2` because it collides with the hidden multiplicity variable.\r\n\r\nIf we enable printing linearity variables, the output is now\r\n```\r\n                   Branch :: forall (n1 :: GHC.Types.Multiplicity) a (n2 :: Peano).\r\n                             a -->.(n1) HTree n2 (HTree ('S n2) a) -->.(n1) HTree ('S n2) a,\r\n```\r\n\r\nso at least `n1` is now bound."}}
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