Add some (mostly trivial) Duoidal instances

.config/project/default.nix

@@ -51,7 +51,10 @@
       ##       i686-linux again …
       programs.prettier.enable = lib.mkForce true;
     };
-    vale.enable = true;
+    vale = {
+      enable = true;
+      vocab.${config.project.name}.accept = ["duoid"];
+    };
   };
 
   ## CI

algebraic-graphs/README.md

@@ -3,12 +3,12 @@
 [![Packaging status](https://repology.org/badge/tiny-repos/haskell:duoids.svg)](https://repology.org/project/haskell:duoids/versions)
 [![latest packaged versions](https://repology.org/badge/latest-versions/haskell:duoids.svg)](https://repology.org/project/haskell:duoids/versions)
 
-Unifying parallel and sequential operations
-
-Duoids relate a pair of monoids, where one can be seen as “parallel” and the other “sequential”.
+[Duoids](https://hackage.haskell.org/package/duoids) applied to the [algebraic-graphs](https://hackage.haskell.org/package/algebraic-graphs) package.
 
 ## usage
 
+There are `Duoid` instances for the various graph representations in `algebraic-graphs`. There are also some implementations of `Duoid` methods to make it easy to provide `Duoid` instances for _other_ `Graph` instances.
+
 ## versioning
 
 This project largely follows the [Haskell Package Versioning Policy](https://pvp.haskell.org/) (PVP), but is more strict in some ways.

core/README.md

@@ -107,12 +107,16 @@ The `async` package has a `Concurrently` newtype over `IO` that’s the same as
 
 ### [either](https://hackage.haskell.org/package/either)
 
-The `either` package has a `Validation` type that’s isomorphic to `Either` and has an applicative instance that’s the same as the `Parallel (Either e)` instance here. However, it doesn’t have anything like the `Duoidal` class, and so requires manual conversion back and forth between `Either` and `Validation`.
+The `either` package has a `Validation` type that’s isomorphic to `Either` and has an `Applicative` instance that’s the same as the `Parallel (Either e)` instance here. However, it doesn’t have anything like the `Duoidal` class, and so requires manual conversion back and forth between `Either` and `Validation`.
 
 ### [Haskerwaul](https://github.com/sellout/haskerwaul#readme)
 
 A broader package that contains a more general (category polymorphic) implementation of duoids. It’s also much less pragmatic.
 
+### [multi-except](https://hackage.haskell.org/package/multi-except)
+
+This seems like another approach to `Validation`, but I haven’t used it.
+
 ### [United Monoids](https://github.com/snowleopard/united)
 
 Andrey Mokhov’s independently-discovered implementation. I think united monoids are normal duoids in **Set**. United Monoids also offers a `Semilattice` class and avoids newtypes by treating the parallel semigroup (`overlay` in United Monoids) as primary, with sequential (`connect`) as an additional operation. It also forces both identities to be the same.

core/duoids.cabal

@@ -137,7 +137,8 @@ common defaults
 
 library
   import: defaults
-  hs-source-dirs: src
+  hs-source-dirs:
+    src
   exposed-modules:
     Control.Duoidal
     Control.Duoidal.Either