added folding to iterators

src/lib.ts

@@ -2,7 +2,21 @@
 export type { Arr, ClassOf, Constructible, Function, InstanceOf, KeyOfType, Tail } from "./lib/types.ts";
 
 // functions
-export { all, chunk, enumerate, fill, filter, filter_map, fold, it, Iter, map, window, zip } from "./lib/iter.ts";
+export {
+	all,
+	chunk,
+	enumerate,
+	fill,
+	filter,
+	filter_map,
+	fold,
+	it,
+	Iter,
+	map,
+	reduce,
+	window,
+	zip,
+} from "./lib/iter.ts";
 export { log_from, next, split_promise, wait } from "./lib/utils.ts";
 
 // Structures

src/lib/iter.ts

@@ -71,12 +71,21 @@ export function* fill<I, O>(iter: Iterable<I>, value: O) {
 	for (const _item of iter) yield value;
 }
 
-export function fold<I, O>(iter: Iterable<I>, init: O, reduction: (item: I, acc: O) => O) {
+export function reduce<I, O>(iter: Iterable<I>, init: O, reduction: (item: I, acc: O) => O) {
 	let accumulator = init;
 	for (const item of iter) accumulator = reduction(item, accumulator);
 	return accumulator;
 }
 
+export function fold<T>(iter: Iterable<T>, reduction: (first: T, next: T) => T) {
+	let accumulator = undefined as T | undefined, passed_first = false;
+	for (const item of iter) {
+		if (passed_first) accumulator = reduction(accumulator!, item);
+		else accumulator = item, passed_first = true;
+	}
+	return accumulator;
+}
+
 export class Iter<T> {
 	iter;
 	[Symbol.iterator] = () => this.iter[Symbol.iterator]();
@@ -136,8 +145,12 @@ export class Iter<T> {
 		return fill(this, value);
 	}
 
-	fold<O>(init: O, reduction: (item: T, acc: O) => O) {
+	fold(reduction: (first: T, next: T) => T) {
-		return fold(this, init, reduction);
+		return fold(this, reduction);
+	}
+
+	reduce<O>(init: O, reduction: (item: T, acc: O) => O) {
+		return reduce(this, init, reduction);
 	}
 }