feat(ch18): add a pipeline for composable custom data types

src/ch-18_composable_data_types/18.1_composable_data_types.js

@@ -0,0 +1,8 @@
+export const t = value => {
+    const add = n => t(value + n);
+
+    return Object.assign(add, {
+        toString: () => `t(${value})`,
+        valueOf: () => value,
+    })
+};

src/ch-18_composable_data_types/18.1_composable_data_types.test.js

@@ -1,16 +1,9 @@
 import {expect} from 'chai';
+import {pipe} from "../ch-10_abstraction-and-composition/10.1_abstraction_and_composition";
+import {t} from './18.1_composable_data_types';
 
 describe("Composable custom Data Types", () => {
     it("should describe a factory that returns instances (functions) of numerical data types", () => {
-        const t = value => {
-            const add = n => t(value + n);
-
-            return Object.assign(add, {
-                toString: () => `t(${value})`,
-                valueOf: () => value,
-            })
-        };
-
         const [x, y, z] = [1, 2, 3];
 
         // Identity
@@ -22,4 +15,16 @@ describe("Composable custom Data Types", () => {
         expect(t(x)(t(y)(t(z))).valueOf()).equal(6);
         expect(t(x)(t(y))(t(z)).valueOf()).equal(t(x)(t(y)(t(z))).valueOf());
     });
+
+    it("should use a pipeline with an initial value", () => {
+        const add = (...fns) => pipe(...fns)(t(0));
+
+        const sum = add(
+            t(4),
+            t(4),
+            t(-1),
+        );
+
+        expect(sum.valueOf()).equal(7);
+    });
 });