Add lesson 7 examples

Author: dmitriz

examples/6-semigroups-types.js

@@ -6,8 +6,8 @@ const {Map} = require('immutable-ext')
 
 // Sum container adds semigroup structure
 // via the 'concat' method
-const Sum = x =>
-({
+const Sum = x => ({
+
   //  make x accessible via 'x' prop
   x,
 
@@ -27,8 +27,7 @@ console.log(
 
 
 // All container add logical (boolean) 'concat'
-const All = x =>
-({
+const All = x => ({
   x,
   concat: ({x: y}) => All(x && y),
 
@@ -43,8 +42,7 @@ console.log(
 
 
 
-const First = x =>
-({
+const First = x => ({
   x,
 
   // throw away the arg and keep our First
@@ -69,7 +67,28 @@ const acct2 = Map({
   friends: ['Gatsby']
 })
 
+
+// The semigroup structure combines both objects componentwise
 // individual custom 'concat' applies in each component
 const res = acct1.concat(acct2)
 
 console.log(res.toJS())
+
+
+
+// from the comments to video
+// x must be an Either
+const FirstEither = x => ({
+  fold: f => x.fold(f, f),
+  concat: o => x.isLeft ? o : First(x)
+})
+
+
+const find = (xs, f) => List(xs)
+  .foldMap(
+    x => FirstEither(f(x) ? Right(x) : Left()),
+    First.empty
+  )
+  .fold(x => x)
+
+

examples/types-semigroups.js renamed to examples/7-semigroups-examples.js

@@ -1,3 +1,5 @@
+const { Map } = require('immutable-ext')
+
 const result = [1,3].concat([4,5]).concat([5,6,7])
 
 console.log(result)
@@ -63,8 +65,6 @@ console.log(resFalse)
 console.log(resTrue)
 
 
-
-
 const First = x =>
 ({
   x,
@@ -79,3 +79,37 @@ const First = x =>
 const resFirst = First("bla").concat(First("last"))
 
 console.log(resFirst)
+
+
+// Wrap each prop into corresponding Semigroup!
+
+// User account 1
+const acc1 = Map({
+
+  // First takes first when combined
+  name: First('Nico'),
+
+  // All applies logical all
+  isPaid: All(true),
+
+  // Sum sums the numbers when combined
+  points: Sum(10),
+
+  // Array already has 'concat' method
+  friends: ['Franklin']
+})
+
+const acc2 = Map({
+  name: First('Nico'),
+  isPaid: All(false),
+  points: Sum(2),
+  friends: ['Gatsby']
+})
+
+const res = acc1.concat(acc2)
+
+console.log(
+  'Combine: ', acc1.toJS(),
+  '\n with: ', acc2.toJS(),
+  '\n yields: ', res.toJS()
+)