ceylon/ceylon-compiler — comment on commit 7f62a11eea451354395089c20b6c5565548f9c1b
File:  line 0
By quintesse:

Hi Tom, talked this over a bit with Gavin and we think this error should have a more specific name, like UnenumeratedTypeError for example, which was Gavin's idea while my suggestion was NonExhaustiveSwitchError. But TypeSystemError just gives the wrong impression, it's not an error of the type system really.