Merge pull request #6 from purescript/docs

Update docs

Author: paf31

README.md

@@ -9,27 +9,46 @@ class Profunctor p where
   dimap :: forall a b c d. (a -> b) -> (c -> d) -> p b c -> p a d
 ```
 
+A `Profunctor` is a `Functor` from the pair category `(Type^op, Type)`
+to `Type`.
+
+In other words, a `Profunctor` is a type constructor of two type
+arguments, which is contravariant in its first argument and covariant
+in its second argument.
+
+The `dimap` function can be used to map functions over both arguments
+simultaneously.
+
+A straightforward example of a profunctor is the function arrow `(->)`.
+
+Laws:
+
+- Identity: `dimap id id = id`
+- Composition: `dimap f1 g1 <<< dimap f2 g2 = dimap (f1 >>> f2) (g1 <<< g2)`
 
 #### `lmap`
 
 ``` purescript
 lmap :: forall a b c p. (Profunctor p) => (a -> b) -> p b c -> p a c
 ```
 
+Map a function over the (contravariant) first type argument only.
 
 #### `rmap`
 
 ``` purescript
 rmap :: forall a b c p. (Profunctor p) => (b -> c) -> p a b -> p a c
 ```
 
+Map a function over the (covariant) second type argument only.
 
 #### `arr`
 
 ``` purescript
 arr :: forall a b p. (Category p, Profunctor p) => (a -> b) -> p a b
 ```
 
+Lift a pure function into any `Profunctor` which is also a `Category`.
 
 #### `profunctorArr`
 
@@ -49,6 +68,12 @@ class (Profunctor p) <= Choice p where
   right :: forall a b c. p b c -> p (Either a b) (Either a c)
 ```
 
+The `Choice` class extends `Profunctor` with combinators for working with
+sum types.
+
+`left` and `right` lift values in a `Profunctor` to act on the `Left` and
+`Right` components of a sum, respectively.
+
 
 #### `choiceArr`
 
@@ -63,13 +88,20 @@ instance choiceArr :: Choice Prim.Function
 (+++) :: forall p a b c d. (Category p, Choice p) => p a b -> p c d -> p (Either a c) (Either b d)
 ```
 
+Compose a value acting on a sum from two values, each acting on one of
+the components of the sum.
 
 #### `(|||)`
 
 ``` purescript
 (|||) :: forall p a b c. (Category p, Choice p) => p a c -> p b c -> p (Either a b) c
 ```
 
+Compose a value which eliminates a sum from two values, each eliminating
+one side of the sum.
+
+This combinator is useful when assembling values from smaller components,
+because it provides a way to support two different types of input.
 
 
 ## Module Data.Profunctor.Strong
@@ -82,6 +114,12 @@ class (Profunctor p) <= Strong p where
   second :: forall a b c. p b c -> p (Tuple a b) (Tuple a c)
 ```
 
+The `Strong` class extends `Profunctor` with combinators for working with
+product types.
+
+`first` and `first` lift values in a `Profunctor` to act on the first and 
+second components of a `Tuple`, respectively.
+
 
 #### `strongArr`
 
@@ -96,9 +134,17 @@ instance strongArr :: Strong Prim.Function
 (***) :: forall p a b c d. (Category p, Strong p) => p a b -> p c d -> p (Tuple a c) (Tuple b d)
 ```
 
+Compose a value acting on a `Tuple` from two values, each acting on one of
+the components of the `Tuple`.
 
 #### `(&&&)`
 
 ``` purescript
 (&&&) :: forall p a b c. (Category p, Strong p) => p a b -> p a c -> p a (Tuple b c)
-```
+```
+
+Compose a value which introduces a `Tuple` from two values, each introducing
+one side of the `Tuple`.
+
+This combinator is useful when assembling values from smaller components,
+because it provides a way to support two different types of output.

src/Data/Profunctor.purs

@@ -1,14 +1,33 @@
 module Data.Profunctor where
 
+  -- | A `Profunctor` is a `Functor` from the pair category `(Type^op, Type)`
+  -- | to `Type`.
+  -- |
+  -- | In other words, a `Profunctor` is a type constructor of two type
+  -- | arguments, which is contravariant in its first argument and covariant
+  -- | in its second argument.
+  -- | 
+  -- | The `dimap` function can be used to map functions over both arguments
+  -- | simultaneously.
+  -- |
+  -- | A straightforward example of a profunctor is the function arrow `(->)`.
+  -- |
+  -- | Laws:
+  -- | 
+  -- | - Identity: `dimap id id = id`
+  -- | - Composition: `dimap f1 g1 <<< dimap f2 g2 = dimap (f1 >>> f2) (g1 <<< g2)`
   class Profunctor p where
     dimap :: forall a b c d. (a -> b) -> (c -> d) -> p b c -> p a d
 
+  -- | Map a function over the (contravariant) first type argument only.
   lmap :: forall a b c p. (Profunctor p) => (a -> b) -> p b c -> p a c
   lmap a2b = dimap a2b id
 
+  -- | Map a function over the (covariant) second type argument only.
   rmap :: forall a b c p. (Profunctor p) => (b -> c) -> p a b -> p a c
   rmap b2c = dimap id b2c
 
+  -- | Lift a pure function into any `Profunctor` which is also a `Category`.
   arr :: forall a b p. (Category p, Profunctor p) => (a -> b) -> p a b
   arr f = rmap f id
 

src/Data/Profunctor/Choice.purs

@@ -3,6 +3,12 @@ module Data.Profunctor.Choice where
   import Data.Either (Either(..), either)
   import Data.Profunctor
 
+  -- | The `Choice` class extends `Profunctor` with combinators for working with
+  -- | sum types.
+  -- |
+  -- | `left` and `right` lift values in a `Profunctor` to act on the `Left` and
+  -- | `Right` components of a sum, respectively.
+  -- |
   class (Profunctor p) <= Choice p where
     left :: forall a b c. p a b -> p (Either a c) (Either b c)
     right :: forall a b c. p b c -> p (Either a b) (Either a c)
@@ -16,9 +22,16 @@ module Data.Profunctor.Choice where
   infixr 2 +++
   infixr 2 ||| 
 
+  -- | Compose a value acting on a sum from two values, each acting on one of
+  -- | the components of the sum.
   (+++) :: forall p a b c d. (Category p, Choice p) => p a b -> p c d -> p (Either a c) (Either b d)
   (+++) l r = left l >>> right r
 
+  -- | Compose a value which eliminates a sum from two values, each eliminating
+  -- | one side of the sum.
+  -- |
+  -- | This combinator is useful when assembling values from smaller components,
+  -- | because it provides a way to support two different types of input.
   (|||) :: forall p a b c. (Category p, Choice p) => p a c -> p b c -> p (Either a b) c 
   (|||) l r = (l +++ r) >>> join
     where

src/Data/Profunctor/Strong.purs

@@ -3,6 +3,12 @@ module Data.Profunctor.Strong where
   import Data.Profunctor
   import Data.Tuple (Tuple(..))
 
+  -- | The `Strong` class extends `Profunctor` with combinators for working with
+  -- | product types.
+  -- |
+  -- | `first` and `first` lift values in a `Profunctor` to act on the first and 
+  -- | second components of a `Tuple`, respectively.
+  -- |
   class (Profunctor p) <= Strong p where
     first :: forall a b c. p a b -> p (Tuple a c) (Tuple b c)
     second :: forall a b c. p b c -> p (Tuple a b) (Tuple a c)
@@ -14,9 +20,16 @@ module Data.Profunctor.Strong where
   infixr 3 ***
   infixr 3 &&&
 
+  -- | Compose a value acting on a `Tuple` from two values, each acting on one of
+  -- | the components of the `Tuple`.
   (***) :: forall p a b c d. (Category p, Strong p) => p a b -> p c d -> p (Tuple a c) (Tuple b d)
   (***) l r = first l >>> second r
 
+  -- | Compose a value which introduces a `Tuple` from two values, each introducing
+  -- | one side of the `Tuple`.
+  -- |
+  -- | This combinator is useful when assembling values from smaller components,
+  -- | because it provides a way to support two different types of output.
   (&&&) :: forall p a b c. (Category p, Strong p) => p a b -> p a c -> p a (Tuple b c)
   (&&&) l r = split >>> (l *** r)
     where