feat(transducers): add peek() xform, update readme

packages/transducers/README.md

@@ -143,7 +143,7 @@ package.
 yarn add @thi.ng/transducers
 ```
 
-Package sizes (gzipped): ESM: 7.8KB / CJS: 8.3KB / UMD: 7.5KB
+Package sizes (gzipped): ESM: 7.8KB / CJS: 8.4KB / UMD: 7.6KB
 
 ## Dependencies
 
@@ -964,6 +964,7 @@ tx.transduce(tx.map((x) => x*10), tx.push(), tx.range(4))
 - [partitionSort](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/partition-sort.ts)
 - [partitionSync](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/partition-sync.ts)
 - [partition](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/partition.ts)
+- [peek](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/peek.ts)
 - [pluck](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/pluck.ts)
 - [rename](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/rename.ts)
 - [sample](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/sample.ts)

packages/transducers/README.tpl.md

@@ -728,6 +728,7 @@ tx.transduce(tx.map((x) => x*10), tx.push(), tx.range(4))
 - [partitionSort](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/partition-sort.ts)
 - [partitionSync](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/partition-sync.ts)
 - [partition](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/partition.ts)
+- [peek](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/peek.ts)
 - [pluck](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/pluck.ts)
 - [rename](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/rename.ts)
 - [sample](https://github.com/thi-ng/umbrella/tree/develop/packages/transducers/src/xform/sample.ts)

packages/transducers/src/index.ts

@@ -77,6 +77,7 @@ export * from "./xform/partition-of";
 export * from "./xform/partition-sort";
 export * from "./xform/partition-sync";
 export * from "./xform/partition";
+export * from "./xform/peek";
 export * from "./xform/pluck";
 export * from "./xform/rename";
 export * from "./xform/sample";

packages/transducers/src/xform/peek.ts

@@ -0,0 +1,21 @@
+import { peek as _peek } from "@thi.ng/arrays";
+import { Transducer } from "../api";
+import { map } from "./map";
+
+/**
+ * Transducer version of {@link @thi.ng/api#peek}, i.e. extracts the
+ * last item of an array.
+ *
+ * @example
+ * ```ts
+ * [...peek([ [1, 2, 3], [4, 5] ])]
+ * // [ 3, 5 ]
+ * ```
+ *
+ * @param src -
+ */
+export function peek<T>(): Transducer<T[], T>;
+export function peek<T>(src: Iterable<T[]>): IterableIterator<T>;
+export function peek<T>(src?: Iterable<T[]>): any {
+    return map(_peek, src!);
+}