haskell@gentoo.org Gentoo Haskell Enisable the use of the `hashable` package. Disabling this may be useful for accelerating builds in sandboxes for expert users. Note: `-hashable` implies `-unordered-containers`, as we are necessarily not able to supply those instances as well. Enable the use of the `containers` package. Disabling this may be useful for accelerating builds in sandboxes for expert users. Enable the use of the `unordered-containers` package. Disabling this may be useful for accelerating builds in sandboxes for expert users. Haskellers are usually familiar with monoids and semigroups. A monoid has an appending operation `<>` (or `mappend`), and an identity element, `mempty`. A semigroup has an appending `<>` operation, but does not require a `mempty` element. A Semiring has two appending operations, `plus` and `times`, and two respective identity elements, `zero` and `one`. More formally, a Semiring R is a set equipped with two binary relations `+` and `*`, such that: (R,+) is a commutative monoid with identity element 0, (R,*) is a monoid with identity element 1, (*) left and right distributes over addition, and multiplication by '0' annihilates R.