feat(sum): Add module sum

Sums a list of numbers using add

src/__tests__/sum.js

@@ -0,0 +1,8 @@
+import { sum } from '../';
+
+describe('Core.sum', () => {
+  test('adds all numbers in a list', () => {
+    expect(sum([1, 2, 3, 4])).toBe(1 + 2 + 3 + 4);
+    expect(sum([-1, -2, -3, -4])).toBe(-1 + -2 + -3 + -4);
+  });
+});

src/index.js

@@ -38,6 +38,7 @@ import reduceRight from './reduceRight';
 import reverse from './reverse';
 import slice from './slice';
 import subtract from './subtract';
+import sum from './sum';
 import T from './T';
 import update from './update';
 import values from './values';
@@ -83,6 +84,7 @@ export {
   reverse,
   slice,
   subtract,
+  sum,
   T,
   update,
   values,

src/sum.js

@@ -0,0 +1,4 @@
+import add from './add';
+import reduce from './reduce';
+
+export default list => reduce(add, 0, list);