This is a joke package. It is meant to show Haskell packages on Hackage can be mutated by revising them. This package uses a custom Cabal setup. It reads the package description, which is what you are reading now, and creates a file at build time from its contents. Since revisions are allowed to change descriptions, the package itself is mutable. I personally disagree with Hackage revisions, so I authored this package to show one way they can be abused. To see how exactly this is accomplished, read the custom setup file on GitHub: https://github.com/tfausak/acme-mutable-package/blob/9ff7cec/Setup.hs.