filter support for inferred type predicates

package.json

@@ -65,7 +65,7 @@
     "debug": "^4.3.7"
   },
   "devDependencies": {
-    "@checkdigit/eslint-config": "^10.0.1",
+    "@checkdigit/eslint-config": "^10.1.0",
     "@checkdigit/jest-config": "^6.0.2",
     "@checkdigit/prettier-config": "^5.5.1",
     "@checkdigit/typescript-config": "^8.0.0",

src/operator/filter.spec.ts

@@ -10,7 +10,7 @@ import { strict as assert } from 'node:assert';
 
 import { describe, it } from '@jest/globals';
 
-import { all, filter, from, pipeline, toArray } from '../index';
+import { all, filter, from, map, pipeline, toArray } from '../index';
 
 describe('filter', () => {
   it('works for an empty array', async () => {
@@ -52,6 +52,19 @@ describe('filter', () => {
     );
   });
 
+  it('supports inferred type predicates', async () => {
+    const iterable = from(['a', 'bb', undefined, 'ccc']);
+    assert.deepEqual(
+      await pipeline(
+        iterable,
+        filter((value) => value !== undefined),
+        map((value) => value.length),
+        toArray,
+      ),
+      [1, 2, 3],
+    );
+  });
+
   it('is chain-able', async () => {
     const iterable = from(['a', 'bb', 'ccc']);
     assert.deepEqual(

src/operator/filter.ts

@@ -10,6 +10,11 @@ import type { Asyncerator } from '../asyncerator';
 
 import type { Operator } from './index';
 
+export default function <Input, Output extends Input>(
+  predicate: (value: Input, index: number) => value is Output,
+): Operator<Input, Output>;
+export default function <Input>(filterFunction: (value: Input, index: number) => boolean): Operator<Input, Input>;
+
 /**
  * Similar to `Array.filter`, only emit values from input for which filterFunction returns true.
  * @param filterFunction