Hi lovely people, I am currently trying to wrap my head around the ambiguity check in GHC. In particular for those two instances: ``` class RowEquality where rowEqual :: Bool instance (1 ~ 2) => RowEquality where rowEqual = True instance ( ("foo" ::: Int & RNil) ~ ("bar" ::: String & "foo" ::: Int & RNil) ) => RowEquality where rowEqual = True ``` I would expect them to behave the same but the second one throws an error when trying to compile the module (*before* using `rowEqual` - that would obviously throw a type error in both cases): ``` Test.hs:24:10: error: • Could not deduce: (| "foo" :: Int |) ~ (| "bar" :: [Char], "foo" :: Int |) from the context: (("foo" ::: Int) & RNil) ~ (("bar" ::: String) & (("foo" ::: Int) & RNil)) bound by an instance declaration: ((("foo" ::: Int) & RNil) ~ (("bar" ::: String) & (("foo" ::: Int) & RNil))) => RowEquality at Test.hs:24:10-94 • In the ambiguity check for an instance declaration To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the instance declaration for 'RowEquality ``` I have troubles to understand why GHC tries to solve the constraint there. I worked through `checkAmbiguity` in `TcValidity` and the function it calls, but from what I can see is that it also tries to solve the `(1 ~ 2)` and fails in the same way as with the second one. I cannot find any reason why the two are treated differently. Thank you Jan