Merge pull request #952 from obsidiansystems/ae@encoder-semigroupoid

Add Semigroupoid instance to Encoder

ChangeLog.md

@@ -22,6 +22,7 @@ This project's release branch is `master`. This log is written from the perspect
 * obelisk-route
   * [#915](https://github.com/obsidiansystems/obelisk/pull/915): Add routeLinkAttr to Obelisk.Route.Frontend. This allows the creation of route links with additional, user-specified attributes.
   * [#918](https://github.com/obsidiansystems/obelisk/pull/918): Add GHC 8.10.7 support for `obelisk-route`
+  * [#952](https://github.com/obsidiansystems/obelisk/pull/952): Add a `Semigroupoid` instance for the `Encoder` type, compatible with its existing `Category` instance.
 * Javascript FFI
   * [#844](https://github.com/obsidiansystems/obelisk/pull/844): Jsaddle FFI example extended in skeleton (example project which is installed by `ob init`). Note the remark on minifier renaming in /skeleton/static/lib.js
   * [#903](https://github.com/obsidiansystems/obelisk/pull/903): Added support for a file which allows users to specify global variables and namespaces in JS, that should not be used by the Google Closure Compiler during minification of the GHCJS produced JS. See the [FAQ](FAQ.md).

lib/route/obelisk-route.cabal

@@ -29,6 +29,7 @@ library
                  ref-tf,
                  reflex,
                  reflex-dom-core,
+                 semigroupoids,
                  template-haskell,
                  tabulation,
                  text,

lib/route/src/Obelisk/Route.hs

@@ -187,6 +187,7 @@ import qualified Data.Map as Map
 import Data.Maybe
 import Data.Set (Set)
 import qualified Data.Set as Set
+import Data.Semigroupoid
 import Data.Some (Some(Some))
 import Data.Tabulation
 import Data.Text (Text)
@@ -373,9 +374,12 @@ checkEncoder :: (Applicative check', Functor check)
   -> check (Encoder check' parse decoded encoded)
 checkEncoder = fmap unsafeMkEncoder . unEncoder
 
+instance (Applicative check, Monad parse) => Semigroupoid (Encoder check parse) where
+  Encoder f `o` Encoder g = Encoder $ liftA2 (.) f g
+
 instance (Applicative check, Monad parse) => Category (Encoder check parse) where
   id = Encoder $ pure id
-  Encoder f . Encoder g = Encoder $ liftA2 (.) f g
+  (.) = o
 
 instance Monad parse => Category (EncoderImpl parse) where
   id = EncoderImpl