Krzysztof Gogolewski authored Apr 09, 2019 and Marge Bot committed Apr 14, 2019

Lint returns a pair (Maybe a, WarnsAndErrs). The Maybe monad
allows to handle an unrecoverable failure.
In case of such a failure, the error should be added to the second
component of the pair. If this is not done, Lint will silently
accept bad programs. This situation actually happened during
development of linear types. This adds a safeguard.