Docs

Author: paf31

README.md

@@ -2,6 +2,10 @@
 
 ## Module Data.Inject
 
+
+This module defines a type class `Inject` which is useful
+when working with coproducts of functors.
+
 #### `Inject`
 
 ``` purescript
@@ -10,27 +14,39 @@ class Inject f g where
   prj :: forall a. g a -> Maybe (f a)
 ```
 
+The `Inject` class asserts a coproduct relationship between two functors.
+
+Specifically, an instance `Inject f g` indicates that `g` is isomorphic to
+a coproduct of `f` and some third functor.
+
+Laws:
+
+- `prj g = Just f` if and only if `inj f = g`
 
 #### `injectReflexive`
 
 ``` purescript
 instance injectReflexive :: Inject f f
 ```
 
+Any functor is isomorphic to the coproduct of itself with the 
+constantly-`Void` functor.
 
 #### `injectLeft`
 
 ``` purescript
 instance injectLeft :: Inject f (Coproduct f g)
 ```
 
+Left injection
 
 #### `injectRight`
 
 ``` purescript
 instance injectRight :: (Inject f g) => Inject f (Coproduct h g)
 ```
 
+Right injection
 
 
 

src/Data/Inject.purs

@@ -1,3 +1,6 @@
+-- | This module defines a type class `Inject` which is useful
+-- | when working with coproducts of functors.
+
 module Data.Inject
   ( Inject
   , inj, prj
@@ -7,18 +10,30 @@ import Data.Either (Either(..))
 import Data.Functor.Coproduct (Coproduct(..), coproduct)
 import Data.Maybe (Maybe(..))
 
+-- | The `Inject` class asserts a coproduct relationship between two functors.
+-- |
+-- | Specifically, an instance `Inject f g` indicates that `g` is isomorphic to
+-- | a coproduct of `f` and some third functor.
+-- | 
+-- | Laws:
+-- | 
+-- | - `prj g = Just f` if and only if `inj f = g`
 class Inject f g where
   inj :: forall a. f a -> g a
   prj :: forall a. g a -> Maybe (f a)
 
+-- | Any functor is isomorphic to the coproduct of itself with the 
+-- | constantly-`Void` functor.
 instance injectReflexive :: Inject f f where
   inj = id
   prj = Just
 
+-- | Left injection
 instance injectLeft :: Inject f (Coproduct f g) where
   inj = Coproduct <<< Left
   prj = coproduct Just (const Nothing)
 
+-- | Right injection
 instance injectRight :: (Inject f g) => Inject f (Coproduct h g) where
   inj = Coproduct <<< Right <<< inj
   prj = coproduct (const Nothing) prj