add creed traverse example

Author: dmitriz

examples/12-creed.js

@@ -1,3 +1,4 @@
+// https://github.com/briancavalier/creed
 const { Promise: CreedPromise } = require('creed')
 
 const launchMissilesCreed = _ =>

examples/22-creed-traversable.js

@@ -0,0 +1,45 @@
+// Native
+const fs = require('fs')
+
+// Packages
+const { List } = require('immutable-ext')
+
+// https://github.com/briancavalier/creed
+// runNode converts Node API with errback into creed promise
+const { runNode, Promise: CreedPromise } = require('creed')
+
+
+// readFilePromise :: String -> String -> Promise Error Buffer
+const readFilePromise = (fileName, encoding = 'utf-8') => 
+	runNode(fs.readFile, fileName, {encoding})
+
+// wrap into List that provides 'traverse'
+const files = List(['file1.txt', 'file2.txt'])
+
+console.log(
+  `Running...
+  List(['file1.txt', 'file2.txt'])
+  	.traverse( CreedPromise.of, readFilePromise )
+  	.then( console.log, console.error ) :
+  `
+)
+
+/*
+	'files' is List of files 'List(a)'
+	'map' preserves the List wrapper, so we can get 'List(Promise(a))'
+	'traverse' applies the function (a -> f b) to each List entry,
+		then lifts the List to Promise of Lists via CreedPromise's 'ap' operator
+		running Promises in parallel!
+*/
+
+files
+  .traverse(
+
+  	// type hint, applicative functor
+  	// needed in case of failure or never running the function
+  	CreedPromise.of, 
+
+  	// traversing function a -> f b
+  	file => readFilePromise(file)
+  )
+	.then( console.log, console.error )

examples/22-leapfrogging-types-traversables.js

@@ -9,7 +9,7 @@ const { List } = require('immutable-ext')
 const FutureTask = require('futurize').futurize(Task)
 
 // (lazy) task to read file
-// FutureTask simply applies to the callback-based function inside
+// FutureTask wraps the callback-based function inside into Task
 const readFileTask = FutureTask(fs.readFile)
 
 // need to wrap into List that provides 'traverse'
@@ -25,7 +25,7 @@ console.log(
 	'files' is List of files 'List(a)'
 	'map' preserves the List wrapper, so we can get List of Tasks 'List(Task(a))'
 	'traverse' applies the function (a -> f b) to each List entry,
-		and wraps all together into single Task of Lists,
+		then lifts the List to Task of Lists via Task's 'ap' operator
 		running the tasks in parallel
 */
 

examples/file1.txt

@@ -0,0 +1 @@
+Hello

examples/file2.txt

@@ -0,0 +1 @@
+World!