{"action":"opened","issue":{"url":"https://api.github.com/repos/mboes/th-lift/issues/20","labels_url":"https://api.github.com/repos/mboes/th-lift/issues/20/labels{/name}","comments_url":"https://api.github.com/repos/mboes/th-lift/issues/20/comments","events_url":"https://api.github.com/repos/mboes/th-lift/issues/20/events","html_url":"https://github.com/mboes/th-lift/issues/20","id":117712199,"number":20,"title":"don't ignore arguments with data kinds","user":{"login":"nfrisby","id":1106131,"avatar_url":"https://avatars.githubusercontent.com/u/1106131?v=3","gravatar_id":"","url":"https://api.github.com/users/nfrisby","html_url":"https://github.com/nfrisby","followers_url":"https://api.github.com/users/nfrisby/followers","following_url":"https://api.github.com/users/nfrisby/following{/other_user}","gists_url":"https://api.github.com/users/nfrisby/gists{/gist_id}","starred_url":"https://api.github.com/users/nfrisby/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nfrisby/subscriptions","organizations_url":"https://api.github.com/users/nfrisby/orgs","repos_url":"https://api.github.com/users/nfrisby/repos","events_url":"https://api.github.com/users/nfrisby/events{/privacy}","received_events_url":"https://api.github.com/users/nfrisby/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":0,"created_at":"2015-11-19T00:17:40Z","updated_at":"2015-11-19T00:17:40Z","closed_at":null,"body":"The current code includes the comment\r\n\r\n    -- Only consider *-kinded type variables, because Lift instances cannot\r\n    -- meaningfully be given to types of other kinds.\r\n\r\nThis comment is explaining how the splice constructs the instance context. It's a reasonable compromise, but it rules out something like the following:\r\n\r\n    data F (b :: Bool) = MkF (If b Float Double)\r\n    $(deriveLift ''F)\r\n\r\nCurrently that splice will fail to compile, because it simply ignores `b`. With this Issue, I request that it instead generate something like the following:\r\n\r\n    instance Lift (If b Float Double) => Lift (F b)\r\n\r\nIn particular, a very robust solution would be to generate a context containing `(Lift T0, Lift T1, ...)` where each `Tn` is the type of one of the data type's constructors' arguments. The downside is that such a naive (but general!) context would be quite noisy and often include redundancies. So perhaps only fallback to this approach for constructor arguments that include an occurrence of a non-`*` type argument."}}