feat: Add complex numbers

No negation (and therefore no subtraction) since that needs self-reference.

test/_pocomath.mjs

@@ -16,4 +16,18 @@ describe('The default full pocomath instance "math"', () => {
       assert.strictEqual(math.negate(-1), 1)
       assert.strictEqual(math.add(10, math.negate(3)), 7)
    })
+
+   it('can be extended', () => {
+      math.install({'add': {
+         '...string': [[], addends => addends.reduce((x,y) => x+y, '')]
+      }})
+      assert.strictEqual(math.add('Kilroy',' is here'), 'Kilroy is here')
+   })
+
+   it('handles complex numbers', () => {
+      const norm13 = {re: 2, im: 3}
+      assert.deepStrictEqual(math.complex(2,3), norm13)
+      assert.deepStrictEqual(math.complex(2), math.complex(2,0))
+      assert.deepStrictEqual(math.add(2, math.complex(0,3)), norm13)
+   })
 })

test/custom.mjs

@@ -0,0 +1,21 @@
+import assert from 'assert'
+import typed from 'typed-function'
+import PocomathInstance from '../PocomathInstance.mjs'
+import * as numbers from '../number/all.mjs'
+import * as complex from '../complex/all.mjs'
+
+const bw = new PocomathInstance('backwards')
+describe('A custom instance', () => {
+   it("works when partially assembled", () => {
+      bw.install(complex)
+      assert.deepStrictEqual(bw.add(2, bw.complex(0, 3)), {re: 2, im: 3})
+   })
+
+   it("can be assembled in any order", () => {
+      bw.install(numbers)
+      typed.addConversion({from: 'string', to: 'number', convert: x => +x})
+      assert.strictEqual(bw.subtract(16, bw.add(3,4,2)), 7)
+      assert.strictEqual(bw.negate('8'), -8)
+      assert.deepStrictEqual(bw.add(bw.complex(1,3), 1), {re: 2, im: 3})
+   })
+})