feat: Add complex numbers

With just the operations we have for numbers, and overall tests.

complex/add.js

@@ -0,0 +1,16 @@
+import { anyComplex } from './complex.js'
+
+export default function create(pmath) {
+    const complex = pmath('complex')
+    return pmath('add', [anyComplex, // naive, but this is just a P-o-C
+       (...addends) => {
+           let sum = complex(addends[0])
+           for (let i = 1; i < addends.length; ++i) {
+               const addend = complex(addends[i])
+               sum.re += addend.re
+               sum.im += addend.im
+           }
+           return sum
+       }])
+}
+                         

complex/all.js

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+import createComplex from './complex.js'
+import createAdd from './add.js'
+import createNegate from './negate.js'
+import createSubtract from '../generic/subtract.js'
+
+export default function create(pmath) {
+   createComplex(pmath)
+   createAdd(pmath)
+   createNegate(pmath)
+   createSubtract(pmath)
+   // not sure if there's anything reasonable to return here
+}

complex/complex.js

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+/* Use a plain object with keys re and im for a complex */
+export function isComplex(z) {
+   return z && typeof z === 'object' && 're' in z && 'im' in z
+}
+
+export function anyComplex(args) {
+   for (let i = 0; i < args.length; ++i) {
+      if (isComplex(args[i])) return true
+   }
+   return false
+}
+
+export default function create(pmath) {
+   const number = pmath('number')
+   return pmath('complex', [
+      [args => args.length == 2, (x,y) => ({re: number(x), im: number(y)})],
+      [args => args.length == 1 && isComplex(args[0]), z => z],
+      [args => args.length == 1, x => ({re: number(x), im: 0})]
+   ])
+}
+

complex/negate.js

@@ -0,0 +1,6 @@
+import { isComplex } from './complex.js'
+
+export default function create(pmath) {
+    return pmath('negate', [args => args.length == 1 && isComplex(args[0]),
+       z => ({re: -z.re, im: -z.im})])
+}