add Endo documentation

src/Endo/README.md

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+# Endo
+
+```haskell
+Endo a
+```
+
+`Endo` is a `Monoid` that will combine (2) functions that have matching domains
+and codomains (endofunctions) under function composition. Due to the nature
+of `Endo` wrapping a function, the underlying value can either be extracted
+using [`valueOf`](#valueof) like any other `Monoid` or can be executed using
+directly using [`runWith`](#runWith), supplying the input.
+
+```javascript
+const Endo = require('crocks/Endo')
+
+const curry = require('crocks/helpers/curry')
+const mconcat = require('crocks/helpers/mconcat')
+const valueOf = require('crocks/pointfree/valueOf')
+
+// add :: Number -> Number -> Number
+const add =
+  x => y => x + y
+
+// multiply :: Number -> Number -> Number
+const multiply =
+  x => y => x * y
+
+// runEndo :: Endo a -> a -> a
+const runEndo =
+  curry(valueOf)
+
+// flow :: Endo Number
+const addAndDouble =
+  Endo(add(10))
+    .concat(Endo(multiply(2)))
+
+// always10 :: Endo Number
+const always10 =
+  mconcat(Endo, [ add(100), multiply(0), add(10) ])
+
+runEndo(addAndDouble, 5)
+//=> 30
+
+always10
+  .runWith(75)
+//=> 10
+```
+
+## Implements
+
+`Semigroup`, `Monoid`
+
+## Constructor Methods
+
+#### empty
+
+```haskell
+Endo.empty :: () -> Endo a
+```
+
+`empty` provides the identity for the `Monoid` in that when the value it
+provides is `concat`ed to any other value, it will return the other value. In
+the case of `Endo` the result of `empty` is the identity function, which echos
+it's input. `empty` is available on both the Constructor and the Instance for
+convenience.
+
+```javascript
+const Endo = require('crocks/Endo')
+
+const runWith = require('crocks/pointfree/runWith')
+
+// empty :: Endo a
+const empty = Endo.empty()
+
+// toUpper :: Endo String
+const toUpper =
+  Endo(x => x.toUpperCase())
+
+// runNice :: Endo String -> String
+const runNice =
+  runWith('nice')
+
+runNice(empty.concat(toUpper))
+//=> "NICE"
+
+runNice(toUpper.concat(empty))
+//=> "NICE"
+```
+
+#### type
+
+```haskell
+Endo.type :: () -> String
+```
+
+`type` provides a string representation of the type name for a given type in
+`crocks`. While it is used mostly internally for law validation, it can be
+useful to the end user for debugging and building out custom types based on the
+standard `crocks` types. While type comparisons can easily be done manually by
+calling `type` on a given type, using the `isSameType` function hides much of
+the boilerplate. `type` is available on both the Constructor and the Instance
+for convenience.
+
+```javascript
+const Endo = require('crocks/Endo')
+const Maybe = require('crocks/Maybe')
+
+const constant = require('crocks/combinators/constant')
+const identity = require('crocks/combinators/identity')
+const isSameType = require('crocks/predicates/isSameType')
+
+Endo.type() //=>  "Endo"
+
+isSameType(Endo, Endo(identity))              //=> true
+isSameType(Endo(identity), Endo(constant(3))) //=> true
+isSameType(Endo(identity), Maybe)             //=> false
+```
+
+## Instance Methods
+
+#### concat
+
+```haskell
+Endo a ~> Endo a -> Endo a
+```
+
+`concat` is used to combine (2) `Semigroup`s of the same type under an operation
+specified by the `Semigroup`. In the case of `Endo`, it will combine (2)
+endofunctions under function composition.
+
+```javascript
+const Endo = require('crocks/Endo')
+
+const assoc = require('crocks/helpers/assoc')
+const mapProps = require('crocks/helpers/mapProps')
+const objOf = require('crocks/helpers/objOf')
+
+// inc :: Number -> Number
+const inc =
+  x => x + 1
+
+// incValue :: Endo Object
+const incValue =
+  Endo(mapProps({ value: inc }))
+
+// addDone :: Endo Object
+const addDone =
+  Endo(assoc('done', true))
+
+// finish :: Endo Object
+const packResults =
+  Endo(objOf('results'))
+
+// finish :: Endo Object
+const finish =
+  incValue.concat(addDone)
+
+finish.runWith({ value: 99 })
+//=> { value: 100, done: true }
+
+finish
+  .concat(packResults)
+  .runWith({ value: 99 })
+//=> { results: { value: 100, done: true } }
+```
+
+#### valueOf
+
+```haskell
+Endo a ~> () -> (a -> a)
+```
+
+`valueOf` is used on all `crocks` `Monoid`s as a means of extraction. While the
+extraction is available, types that implement `valueOf` are not necessarily a
+`Comonad`. This function is used primarily for convenience for some of the
+helper functions that ship with `crocks`. Calling `valueOf` on
+an `Endo` instance will result in the underlying endofunction.
+
+```javascript
+const Endo = require('crocks/Endo')
+
+const filter = require('crocks/pointfree/filter')
+const map = require('crocks/pointfree/map')
+const mconcat = require('crocks/helpers/mconcat')
+
+// lt10 :: [ Number ] -> [ Number ]
+const lt10 =
+  filter(x => x < 10)
+
+// double :: [ Number ] -> [ Number ]
+const double =
+  map(x => x * 2)
+
+// buildEndo :: [ (a -> a) ] -> Endo a
+const buildEndo =
+  mconcat(Endo)
+
+// fn :: [ Number ] -> [ Number ]
+const fn =
+  buildEndo([ lt10, double ])
+    .valueOf()
+
+fn([ 12, 5, 3, 90 ])
+//=> [ 10, 6 ]
+
+fn([])
+//=> []
+```
+
+#### runWith
+
+```haskell
+Endo a ~> a -> a
+```
+
+`Endo` wraps a function and as such, it's underlying endofunction can be run
+while inside of an `Endo` by calling `runWith`. Providing a valid value  of the
+same type required by the function, `runWith` will execute the underlying
+function and return the result.
+
+```javascript
+const Endo = require('crocks/Endo')
+
+const filter = require('crocks/pointfree/filter')
+const map = require('crocks/pointfree/map')
+const mconcat = require('crocks/helpers/mconcat')
+
+// lt10 :: [ Number ] -> [ Number ]
+const lt10 =
+  filter(x => x < 10)
+
+// double :: [ Number ] -> [ Number ]
+const double =
+  map(x => x * 2)
+
+// buildEndo :: [ (a -> a) ] -> Endo a
+const flow =
+  mconcat(Endo, [ lt10, double ])
+
+flow
+  .runWith([ 12, 5, 3, 90 ])
+//=> [ 10, 6 ]
+
+flow
+  .runWith([])
+//=> []
+```