Add shared folder

shared/index.ts

@@ -0,0 +1,109 @@
+/**
+ * PhantomData akin to Rust, because sometimes you need to be smarter than
+ * the compiler.
+ */
+export class PhantomData<P> { private __PHANTOM__: P }
+
+/**
+ * Opaque type, similar to `opaque type` in Flow, or new types in Rust/C.
+ * These should be produced only by manually casting `t as Opaque<T, P>`.
+ *
+ * `P` can be anything as it's never actually used. Using strings is okay:
+ *
+ * ```
+ * type MyType = Opaque<number, 'MyType'>;
+ * ```
+ */
+export type Opaque<T, P> = T & PhantomData<P>;
+
+/**
+ * Just a readable shorthand for null-ish-able types, akin to `T?` in Flow.
+ */
+export type Maybe<T> = T | null | undefined;
+
+/**
+ * Higher order function producing new auto-incremented `Id`s.
+ */
+export function idGenerator<T>(): () => Id<T> {
+    let current = 0;
+
+    return () => current++ as Id<T>;
+}
+
+/**
+ * Unique type-constrained Id number.
+ */
+export type Id<T> = Opaque<number, T>;
+
+interface HasId<T> {
+    id: Id<T>;
+}
+
+export class IdSet<T> {
+    private map: Map<Id<T>, T> = new Map();
+
+    public add(item: T & HasId<T>) {
+        this.map.set(item.id, item);
+    }
+
+    public remove(item: T & HasId<T>) {
+        this.map.delete(item.id);
+    }
+
+    public get entries(): IterableIterator<T> {
+        return this.map.values();
+    }
+}
+
+export function* map<T, U>(iter: IterableIterator<T>, fn: (item: T) => U): IterableIterator<U> {
+    for (const item of iter) yield fn(item);
+}
+
+export function* chain<T>(a: IterableIterator<T>, b: IterableIterator<T>): IterableIterator<T> {
+    yield* a;
+    yield* b;
+}
+
+export function* zip<T, U>(a: IterableIterator<T>, b: IterableIterator<U>): IterableIterator<[T, U]> {
+    let itemA = a.next();
+    let itemB = b.next();
+
+    while (!itemA.done && !itemB.done) {
+        yield [itemA.value, itemB.value];
+
+        itemA = a.next();
+        itemB = b.next();
+    }
+}
+
+export function* take<T>(iter: IterableIterator<T>, n: number): IterableIterator<T> {
+    for (const item of iter) {
+        if (n-- === 0) return;
+
+        yield item;
+    }
+}
+
+export function skip<T>(iter: IterableIterator<T>, n: number): IterableIterator<T> {
+    while (n-- !== 0 && !iter.next().done) {}
+
+    return iter;
+}
+
+export function reduce<T, R>(iter: IterableIterator<T>, fn: (accu: R, item: T) => R, accumulator: R): R {
+    for (const item of iter) accumulator = fn(accumulator, item);
+
+    return accumulator;
+}
+
+export function join(iter: IterableIterator<{ toString: () => string }>, glue: string): string {
+    const first = iter.next();
+
+    if (first.done) return '';
+
+    let result = first.value.toString();
+
+    for (const item of iter) result += glue + item;
+
+    return result;
+}