reformat

Author: dmitriz

examples/25-apply-natural-transformations.js

@@ -4,13 +4,16 @@ const { List } = require('immutable-ext')
 
 const Task = require('data.task')
 
-// 'chain' does not exist on the array,
+// 'chain' (aka 'flatMap') does not exist on the array,
 // so we apply natural transformation into the List first
+// array -> List(array) is a natural transformation, it changes structure but not content
 const res = List(['hello', 'world'])
   .chain( x => List(x.split('')) )
 
-console.log(
-  `List(['hello', 'world']).chain( x => List(x.split('')) ) : `,
+console.log(`
+  List(['hello', 'world'])
+    .chain( x => List(x.split('')) ) : 
+  `,
   res
 )
 
@@ -28,33 +31,36 @@ const larger = x =>
   x * 2
 
 
-const app = xs =>
+// 'first' is a natural transform, so it commutes with 'map'
+// 'first' changes structure but not content
+// 'map' is functor transform, it changes content but not structure
 
+const app = xs =>
   // map, then first
   first(
     largeNumbers(xs)
-    .map(larger)
+      .map(larger)
   )
 
-console.log(
-  `app([2, 400, 5, 1000]) : `,
+console.log(`
+  app([2, 400, 5, 1000]) : `,
   app([2, 400, 5, 1000])
 )
 
 const app1 = xs =>
-
   // first, then map
-  first(
-    largeNumbers(xs)
-  )
-  .map(larger)
+  first(largeNumbers(xs))
+    .map(larger)
 
-console.log(
-  `app1([2, 400, 5, 1000]) : `,
+console.log(`
+  app1([2, 400, 5, 1000]) : `,
   app1([2, 400, 5, 1000])
 )
 
 
+
+// --- Database Example --- //
+
 // fake user returned by id for testing purposes
 const fake = id => ({
   id: id,
@@ -77,12 +83,25 @@ const eitherToTask = e =>
 
 // valid user (id > 2)
 // -> Task returns Either
-console.log(`Db.find(3).chain(eitherToTask).fork(..., ...) : `)
+console.log(`
+  Db.find(3)
+    .chain(eitherToTask)
+    .fork(..., ...) : `
+)
+
+// -> Task(Either(res))
 Db.find(3)
+  // -> Task(res)
   .chain(eitherToTask)
   .fork(console.error, console.log)
 
-console.log(`Db.find(3).chain(eitherToTask).chain(user => Db.find(user.best_friend_id)).chain(eitherToTask).fork(..., ...) : `)
+console.log(`
+  Db.find(3)
+    .chain(eitherToTask)
+    .chain(user => Db.find(user.best_friend_id))
+    .chain(eitherToTask)
+    .fork(..., ...) : `
+)
 
 Db.find(3)
 
@@ -101,14 +120,17 @@ Db.find(3)
 .fork(console.error, console.log)
 
 
-console.log(`Db.find(2).chain(eitherToTask).chain(user => Db.find(user.best_friend_id)).chain(eitherToTask).fork(..., ...) : `)
+console.log(`
+  Db.find(2)
+    .chain(eitherToTask)
+    .chain(user => Db.find(user.best_friend_id))
+    .chain(eitherToTask)
+    .fork(..., ...) : `
+)
 
 // invalid user (id = 2)
 Db.find(2)
 .chain(eitherToTask)
 .chain(user => Db.find(user.best_friend_id))
 .chain(eitherToTask)
 .fork(console.error, console.log)
-
-
-