error_type_unk.nit:22,17--20: Error: class `Fail` not found in module `error_type_unk`.
error_type_unk.nit:23,9: Error: method `+` does not exists in `Bool`.
error_type_unk.nit:24,16--19: Error: class `Fail` not found in module `error_type_unk`.