haskell@gentoo.org Gentoo Haskell Haskell 98 contravariant functors Get Safe guarantees rather than merely Trustworthy, but with worse constant factors. You can disable the use of the `semigroups` package using `-f-semigroups`. Disabling this is an unsupported configuration, but it may be useful for accelerating builds in sandboxes for expert users. You can disable the use of the `StateVar` package using `-f-StateVar`. Disabling this is an unsupported configuration, but it may be useful for accelerating builds in sandboxes for expert users. You can disable the use of the `tagged` package on older versons of GHC using `-f-tagged`. Disabling this is an unsupported configuration, but it may be useful for accelerating builds in sandboxes for expert users. ekmett/contravariant