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diff --git a/dev-haskell/semigroupoids/metadata.xml b/dev-haskell/semigroupoids/metadata.xml new file mode 100644 index 000000000000..0b9dfed4ec37 --- /dev/null +++ b/dev-haskell/semigroupoids/metadata.xml @@ -0,0 +1,61 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd"> +<pkgmetadata> + <herd>haskell</herd> + <longdescription> + Provides a wide array of semigroupoids and operations for working with semigroupds. + + A Semigroupoid is a Category without the requirement of identity arrows for every object in the category. + + When working with comonads you often have the @\<*\>@ portion of an @Applicative@, but + not the @pure@. This was captured in Uustalu and Vene's \"Essence of Dataflow Programming\" + in the form of the @ComonadZip@ class in the days before @Applicative@. Apply provides a weaker invariant, but for the comonads used for data flow programming (found in the streams package), this invariant is preserved. Applicative function composition forms a semigroupoid. + + Similarly many structures are nearly a comonad, but not quite, for instance lists provide a reasonable 'extend' operation in the form of 'tails', but do not always contain a value. + + + Ideally the following relationships would hold: + + > Traversable <---- Foldable <--- Functor ------> Alt ---------> Plus Semigroupoid + > | | | | | + > v v v v v + > Traversable1 <--- Foldable1 Apply --------> Applicative -> Alternative Category + > | | | | + > v v v v + > Bind ---------> Monad -------> MonadPlus Arrow + > + + Apply, Bind, and Extract give rise the Static, Kleisli and Cokleisli semigroupoids respectively. + + This lets us remove many of the restrictions from various monad transformers + as in many cases the binding operation or @\<*\>@ operation does not require them. + + Finally, to work with these weaker structures it is beneficial to have containers + that can provide stronger guarantees about their contents, so versions of 'Traversable' + and 'Foldable' that can be folded with just a 'Semigroup' are added. + </longdescription> + <use> + <flag name="comonad">You can disable the use of the `comonad` package using + `-f-comonad`. Disabling this is an unsupported configuration, but it may be + useful for accelerating builds in sandboxes for expert users. If disabled we + will not supply instances of `Comonad`</flag> + <flag name="containers">You can disable the use of the `containers` package + using `-f-containers`. Disabing this is an unsupported configuration, but it + may be useful for accelerating builds in sandboxes for expert users.</flag> + <flag name="contravariant">You can disable the use of the `contravariant` + package using `-f-contravariant`. Disabling this is an unsupported + configuration, but it may be useful for accelerating builds in sandboxes for + expert users. If disabled we will not supply instances of `Contravariant`</flag> + <flag name="distributive">You can disable the use of the `distributive` + package using `-f-distributive`. Disabling this is an unsupported + configuration, but it may be useful for accelerating builds in sandboxes for + expert users. If disabled we will not supply instances of `Distributive`</flag> + <flag name="tagged">You can disable the use of the `tagged` package + using `-f-tagged`. Disabing this is an unsupported + configuration, but it may be useful for accelerating builds in + sandboxes for expert users.</flag> + </use> + <upstream> + <remote-id type="github">ekmett/semigroupoids</remote-id> + </upstream> +</pkgmetadata> |