feat: Invalidation and lazy reloading of implementations

The interface is a bit clunky, the "author" and the callback "data"
  have to be specified when adding (an) implementation(s) in order
  for this to work. But it does, and this is just a PoC, the interface
  could be cleaned up.

generic/subtract.js

@@ -4,6 +4,6 @@ export default function create(pmath) {
    return pmath(
       'subtract',
       [args => args.length === 2, (x, y) => add(x, negate(y))],
-      create)
+      create, pmath)
    return pmath.subtract
 }

picomathInstance.js

@@ -6,11 +6,11 @@ export default function picomathInstance (instName) {
      * as a function, it takes a name and 0 or more implementations add adds
      * them to its poortf property named name, returning that property value.
      */
-    function fn (name, imps, author) {
+    function fn (name, imps, author, data) {
         if (name in fn) {
-            fn[name].addImps(imps, author)
+            fn[name].addImps(imps, author, data)
         } else {
-            fn[name] = poortf(name, imps, author)
+            fn[name] = poortf(name, imps, author, data)
         }
         return fn[name]
     }

poortf.js

@@ -7,23 +7,27 @@
 const addImps = (dest, imps, author) => {
    if (imps) {
       if (!Array.isArray(imps[0])) imps = [imps]
-      if (author) {
+   } else {
-         if (dest.authors.has(author)) {
+      imps = []
-            const [count, index] = dest.authors.get(author)
-            if (count) dest.imps.splice(index, count)
-         }
-         dest.authors.set(author, [imps.length, dest.imps.length])
-      }
-      for (const imp of imps) dest.imps.push(imp)
    }
+   if (author) {
+      if (dest.authors.has(author)) {
+         const [count, index] = dest.authors.get(author)
+         if (count) dest.imps.splice(index, count)
+      }
+      dest.authors.set(author, [imps.length, dest.imps.length])
+   }
+   for (const imp of imps) dest.imps.push(imp)
 }
+
 /* Create a TF, optionally adding some initial imps and further optionally
  * registering them to an author. There are two advantages to author
  * registration: (1) if the same author adds implementations, the prior imps
  * will be deleted, and (2) the author can be invalidated, and the TF will
- * lazily call the author back the next time it is called to re-add the imps.
+ * lazily call the author back with the given data the next time it is 
+ * called, so that it can re-add the imps.
  */
-export default function poortf (name, imps, author) {
+export default function poortf (name, imps, author, data) {
    /* This is the (function) object we will return */
    function fn () {
       for (const imp of fn.imps) {
@@ -37,9 +41,39 @@ export default function poortf (name, imps, author) {
    Object.defineProperty(fn, 'name', {value: name})
    fn.imps = []
    fn.authors = new Map() // tracks who made each implementation
+   fn.authorData = new Map() // tracks author callback data
    addImps(fn, imps, author)
-   fn.addImps = (newI, author) => addImps(fn, newI, author)
+   if (author) fn.authorData.set(author, data)
-
+   fn.addImps = (newI, author, data) => {
+      addImps(fn, newI, author)
+      if (author) fn.authorData.set(author, data)
+   }
+   fn.invalidate = author => {
+      addImps(fn, null, author) // deletes the author's imps
+      fn.unshiftImp([() => true, (...args) => fn.reloadAndRecall(args)])
+   }
+   fn.unshiftImp = newImp => {
+      fn.imps.unshift(newImp)
+      for (const record in fn.authors.values()) {
+         record[1] += 1
+      }
+   }
+   fn.shiftImp = () => {
+      const oldImp = fn.imps.shift()
+      for (const record in fn.authors.values()) {
+         record[1] -= 1
+      }
+   }
+   fn.reloadAndRecall = (argArray) => {
+      fn.shiftImp() // throw ourself away, ha ha
+      for (const author of fn.authorData.keys()) {
+         if (fn.authors.get(author)[0] === 0) {
+            // imps count of 0 means the author was invalidated
+            author(fn.authorData.get(author))
+         }
+      }
+      return fn.apply(null, argArray)
+   }
    return fn
 }
 

test/_poortf.js

@@ -21,13 +21,22 @@ describe('poortf', () => {
       assert.throws(() => add('kilroy'), TypeError)
    })
 
+   const defNumber = what => {
+      slate.addImps([args => typeof args[0] === 'number',
+                     n => 'I am not number ' + (what+n)],
+                    defNumber, what+1)
+   }
+   
    it('extends an empty tf', () => {
+      defNumber(2)
+      assert.strictEqual(slate(0, 'was here'), 'I am not number 2')
+      assert.throws(() => slate('Kilroy', 'was here'), TypeError)
       slate.addImps([
          [args => typeof args[0] === 'string', s => s + ' wuz here'],
-         [args => typeof args[0] === 'number', () => 'I am not a number']
+         [args => typeof args[0] === 'boolean', () => 'Maybe I am a number']
       ])
       assert.strictEqual(slate('Kilroy', 'was here'), 'Kilroy wuz here')
-      assert.strictEqual(slate(2, 'was here'), 'I am not a number')
+      assert.strictEqual(slate(true), 'Maybe I am a number')
       assert.throws(() => slate(['Ha!']), TypeError)
    })
 
@@ -36,6 +45,15 @@ describe('poortf', () => {
       assert.strictEqual(add('Kilroy', 23), 'Kilroy23')
       assert.throws(() => add(['Ha!'], 'gotcha'), TypeError)
    })
+   
+   it('can invalidate and lazily reload implementations', () => {
+      slate.invalidate(defNumber)
+      assert.strictEqual(slate.imps.length, 3) // reloader plus two non-number
+      assert.strictEqual(slate(1), 'I am not number 4') // 'what' is now 3!!
+      assert.strictEqual(slate('Yorlik', 7), 'Yorlik wuz here')
+      assert.strictEqual(slate(false), 'Maybe I am a number')
+      assert.strictEqual(slate.imps.length, 3) // reloader gone
+   })
 })