Merge pull request #13 from purescript/invariant

Add invariant instances

Author: garyb

bower.json

@@ -16,6 +16,7 @@
     "package.json"
   ],
   "dependencies": {
-    "purescript-arrays": "~0.4.0"
+    "purescript-arrays": "~0.4.0",
+    "purescript-invariant": "~0.1.0"
   }
 }

docs/Data.Monoid.Additive.md

@@ -86,6 +86,13 @@ instance comonadAdditive :: Comonad Additive
 ```
 
 
+#### `invariantAdditive`
+
+``` purescript
+instance invariantAdditive :: Invariant Additive
+```
+
+
 #### `showAdditive`
 
 ``` purescript

docs/Data.Monoid.Dual.md

@@ -86,6 +86,13 @@ instance comonadDual :: Comonad Dual
 ```
 
 
+#### `invariantDual`
+
+``` purescript
+instance invariantDual :: Invariant Dual
+```
+
+
 #### `showDual`
 
 ``` purescript

docs/Data.Monoid.Endo.md

@@ -24,6 +24,13 @@ runEndo :: forall a. Endo a -> a -> a
 ```
 
 
+#### `invariantEndo`
+
+``` purescript
+instance invariantEndo :: Invariant Endo
+```
+
+
 #### `semigroupEndo`
 
 ``` purescript

docs/Data.Monoid.First.md

@@ -81,6 +81,13 @@ instance extendFirst :: Extend First
 ```
 
 
+#### `invariantFirst`
+
+``` purescript
+instance invariantFirst :: Invariant First
+```
+
+
 #### `showFirst`
 
 ``` purescript

docs/Data.Monoid.Last.md

@@ -81,6 +81,13 @@ instance extendLast :: Extend Last
 ```
 
 
+#### `invariantLast`
+
+``` purescript
+instance invariantLast :: Invariant Last
+```
+
+
 #### `showLast`
 
 ``` purescript

docs/Data.Monoid.Multiplicative.md

@@ -72,17 +72,24 @@ instance monadMultiplicative :: Monad Multiplicative
 ```
 
 
-#### `extendAdditive`
+#### `extendMultiplicative`
 
 ``` purescript
-instance extendAdditive :: Extend Multiplicative
+instance extendMultiplicative :: Extend Multiplicative
 ```
 
 
-#### `comonadAdditive`
+#### `comonadMultiplicative`
 
 ``` purescript
-instance comonadAdditive :: Comonad Multiplicative
+instance comonadMultiplicative :: Comonad Multiplicative
+```
+
+
+#### `invariantMultiplicative`
+
+``` purescript
+instance invariantMultiplicative :: Invariant Multiplicative
 ```
 
 

src/Data/Monoid/Additive.purs

@@ -2,6 +2,7 @@ module Data.Monoid.Additive where
 
 import Control.Comonad (Comonad)
 import Control.Extend (Extend)
+import Data.Functor.Invariant (Invariant, invmap)
 import Data.Monoid
 
 -- | Monoid and semigroup for semirings under addition.
@@ -42,6 +43,9 @@ instance extendAdditive :: Extend Additive where
 instance comonadAdditive :: Comonad Additive where
   extract = runAdditive
 
+instance invariantAdditive :: Invariant Additive where
+  invmap f _ (Additive x) = Additive (f x)
+
 instance showAdditive :: (Show a) => Show (Additive a) where
   show (Additive a) = "Additive (" ++ show a ++ ")"
 

src/Data/Monoid/Dual.purs

@@ -2,6 +2,7 @@ module Data.Monoid.Dual where
 
 import Control.Comonad (Comonad)
 import Control.Extend (Extend)
+import Data.Functor.Invariant (Invariant, invmap)
 import Data.Monoid
 
 -- | The dual of a monoid.
@@ -42,6 +43,9 @@ instance extendDual :: Extend Dual where
 instance comonadDual :: Comonad Dual where
   extract = runDual
 
+instance invariantDual :: Invariant Dual where
+  invmap f _ (Dual x) = Dual (f x)
+
 instance showDual :: (Show a) => Show (Dual a) where
   show (Dual a) = "Dual (" ++ show a ++ ")"
 

src/Data/Monoid/Endo.purs

@@ -1,5 +1,6 @@
 module Data.Monoid.Endo where
 
+import Data.Functor.Invariant (Invariant, invmap)
 import Data.Monoid
 
 -- | Monoid of endomorphisms under composition.
@@ -14,6 +15,9 @@ newtype Endo a = Endo (a -> a)
 runEndo :: forall a. Endo a -> a -> a
 runEndo (Endo f) = f
 
+instance invariantEndo :: Invariant Endo where
+  invmap ab ba (Endo f) = Endo (ab <<< f <<< ba)
+
 instance semigroupEndo :: Semigroup (Endo a) where
   (<>) (Endo f) (Endo g) = Endo (f <<< g)