{
  "$type": "site.standard.document",
  "bskyPostRef": {
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    "uri": "at://did:plc:pi6woz4d47bkuws673w2il2r/app.bsky.feed.post/3mijm53j22cz2"
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  "path": "/t/type-equality-in-gadt-typefamily-context/13876#post_2",
  "publishedAt": "2026-04-02T16:15:49.000Z",
  "site": "https://discourse.haskell.org",
  "textContent": "It’s failing in the case\n\n\n       Nothing ->   l\n\n\nand it needs to know\n\n\n    Pop (x : l) c ~ (x : l)\n\n\nand it seems like it _should_ be able to know that because we’ve demonstrated that `x` is _not_ `c`, so we “should” fall through to the\n\n\n      Pop m         c  = m\n\n\nwhere `m ~ (x : l)`. I guess you need something like a “type _in_ equality” constraint in the `Nothing` branch, but I don’t think those exist!",
  "title": "Type equality in GADT/TypeFamily context"
}