diff --git a/package-lock.json b/package-lock.json
index f9f9aab..5393295 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,7 +11,8 @@
       "devDependencies": {
         "@apeleghq/esbuild-plugin-closure-compiler": "^1.0.8",
         "esbuild": "^0.25.3",
-        "folktest": "git+https://git.kitsu.cafe/rowan/folktest.git"
+        "folktest": "git+https://git.kitsu.cafe/rowan/folktest.git",
+        "typescript": "^5.8.3"
       }
     },
     "node_modules/@apeleghq/esbuild-plugin-closure-compiler": {
@@ -814,6 +815,20 @@
         "node": ">=8"
       }
     },
+    "node_modules/typescript": {
+      "version": "5.8.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.8.3.tgz",
+      "integrity": "sha512-p1diW6TqL9L07nNxvRMM7hMMw4c5XOo/1ibL4aAIGmSAt9slTE1Xgw5KWuof2uTOvCg9BY7ZRi+GaF+7sfgPeQ==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "tsc": "bin/tsc",
+        "tsserver": "bin/tsserver"
+      },
+      "engines": {
+        "node": ">=14.17"
+      }
+    },
     "node_modules/util-deprecate": {
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/util-deprecate/-/util-deprecate-1.0.2.tgz",
diff --git a/package.json b/package.json
index 856a9c8..2072ec0 100644
--- a/package.json
+++ b/package.json
@@ -14,6 +14,7 @@
   "devDependencies": {
     "@apeleghq/esbuild-plugin-closure-compiler": "^1.0.8",
     "esbuild": "^0.25.3",
-    "folktest": "git+https://git.kitsu.cafe/rowan/folktest.git"
+    "folktest": "git+https://git.kitsu.cafe/rowan/folktest.git",
+    "typescript": "^5.8.3"
   }
 }
diff --git a/src/index.d.ts b/src/index.d.ts
new file mode 100644
index 0000000..c0b760f
--- /dev/null
+++ b/src/index.d.ts
@@ -0,0 +1,188 @@
+type Nullable<T> = T | null | undefined;
+export interface Predicate<T> {
+    (value: Nullable<T>, index: number): boolean;
+}
+export interface Reducer<T, U = T> {
+    (accumulator: U, value: Nullable<T>, index: number): U;
+}
+export interface Morphism<T, U = T> {
+    (value: Nullable<T>, index: number): U;
+}
+export interface IEnumerator<T> {
+    get current(): Nullable<T>;
+    moveNext(): boolean;
+    reset(): void;
+    toIterator<T>(): Iterator<T>;
+}
+export interface IEnumerable<T> {
+    enumerator(): IEnumerator<T>;
+}
+export interface IEnumeratorFactory<T> {
+    (iterator: Iterator<T>): IEnumerator<T>;
+}
+export declare function isIterable(value: any): value is Iterable<any>;
+export declare function isIterator(value: any): value is Iterator<any>;
+export declare function isBuffer(value: any): value is ArrayBufferLike;
+export declare function isArrayLike(value: any): value is ArrayLike<any>;
+export declare class IteratorEnumerator<T> implements IEnumerator<T>, Iterator<T> {
+    private _iterator;
+    private _consumed;
+    private _current;
+    get current(): Nullable<T>;
+    constructor(iterator: Iterator<T>);
+    static from<T>(iterator: Iterator<T>): IteratorEnumerator<T>;
+    moveNext(): boolean;
+    reset(): void;
+    toIterator<T>(): Iterator<T>;
+    next(...[_value]: [] | [any]): IteratorResult<T>;
+    return(value?: any): IteratorResult<T, any>;
+    throw(e?: any): IteratorResult<T, any>;
+}
+export declare class CachedIteratorEnumerator<T> implements IEnumerator<T>, Iterator<T> {
+    private _iterator;
+    private _cache;
+    private _index;
+    get current(): Nullable<T>;
+    constructor(iterator: Iterator<T>);
+    static from<T>(iterator: Iterator<T>): CachedIteratorEnumerator<T>;
+    moveNext(): boolean;
+    reset(): void;
+    toIterator<T>(): Iterator<T>;
+    next(...[_value]: [] | [any]): IteratorResult<T>;
+    return?(value?: any): IteratorResult<T, any>;
+    throw(e?: any): IteratorResult<T, any>;
+}
+export declare class IterableEnumerator<T> implements IEnumerator<T>, Iterator<T> {
+    private _iterable;
+    private _factory;
+    private _enumerator;
+    get current(): Nullable<T>;
+    constructor(iterable: Iterable<T>, factory?: IEnumeratorFactory<T>);
+    static fromIterable<T>(iterable: Iterable<T>, factory?: IEnumeratorFactory<T>): IEnumerator<T>;
+    moveNext(): boolean;
+    _createIterator(): Iterator<T>;
+    _createEnumerator(): IEnumerator<T>;
+    reset(): void;
+    toIterator<T>(): Iterator<T>;
+    next(...[_value]: [] | [any]): IteratorResult<T, any>;
+    return?(value?: any): IteratorResult<T, any>;
+    throw?(e?: any): IteratorResult<T, any>;
+}
+type ArrayType<T extends ArrayLike<any> | ArrayBufferView> = T extends ArrayLike<infer U> ? U : T extends ArrayBufferTypes ? number : never;
+export declare class ArrayEnumerator<T> implements IEnumerator<T>, Iterator<T>, Iterable<T> {
+    private _array;
+    private _index;
+    get current(): Nullable<T>;
+    constructor(array: ArrayLike<T>);
+    static from<A extends ArrayLike<any> | ArrayBufferView>(array: A): ArrayEnumerator<ArrayType<A>>;
+    [Symbol.iterator](): Iterator<T>;
+    setIndex(index: number): void;
+    moveNext(): boolean;
+    reset(): void;
+    toIterator<T>(): Iterator<T>;
+    next(...[_value]: [] | [any]): IteratorResult<T, any>;
+    return?(_value?: any): IteratorResult<T, any>;
+    throw?(_e?: any): IteratorResult<T, any>;
+}
+export declare class Enumerator<T> implements IEnumerator<T>, Iterator<T> {
+    protected _enumerator: IEnumerator<T>;
+    protected _index: number;
+    get current(): Nullable<T>;
+    constructor(enumerator: IEnumerator<T>);
+    static fromIterable<T>(iterable: Iterable<T>): IEnumerator<T>;
+    static fromIterator<T>(iterator: Iterator<T>, cache?: boolean): IEnumerator<T>;
+    static toIterator<T>(enumerator: IEnumerator<T>): Iterator<T>;
+    [Symbol.iterator](): Iterator<unknown, any, any>;
+    toIterator<T>(): Iterator<T>;
+    moveNext(): boolean;
+    reset(): void;
+    next(...[_value]: [] | [any]): IteratorResult<T, any>;
+    return?(_value?: any): IteratorResult<T, any>;
+    throw?(_e?: any): IteratorResult<T, any>;
+}
+export declare class HelperEnumerator<T> implements IEnumerator<T>, Iterator<T> {
+    protected _enumerator: IEnumerator<T>;
+    protected _index: number;
+    get current(): Nullable<T>;
+    constructor(enumerator: IEnumerator<T>);
+    static toIterator<T>(enumerator: IEnumerator<T>): Iterator<T>;
+    [Symbol.iterator](): Iterator<unknown, any, any>;
+    toIterator<T>(): Iterator<T>;
+    moveNext(): boolean;
+    reset(): void;
+    next(...[_value]: [] | [any]): IteratorResult<T, any>;
+    return?(_value?: any): IteratorResult<T, any>;
+    throw?(_e?: any): IteratorResult<T, any>;
+}
+export declare class DropEnumerator<T> extends HelperEnumerator<T> {
+    private _limit;
+    constructor(enumerator: IEnumerator<T>, limit: number);
+    moveNext(): boolean;
+}
+export declare class FilterEnumerator<T> extends HelperEnumerator<T> {
+    private _filter;
+    constructor(enumerator: IEnumerator<T>, filter: Predicate<T>);
+    moveNext(): boolean;
+}
+export declare class FlatMapEnumerator<T, U = T> implements IEnumerator<U> {
+    private _enumerator;
+    private _flatMap;
+    private _inner?;
+    private _index;
+    constructor(enumerator: IEnumerator<T>, flatMap: Morphism<T, IEnumerator<U>>);
+    get current(): Nullable<U>;
+    moveNext(): boolean;
+    reset(): void;
+    toIterator<T>(): Iterator<T>;
+}
+export declare class MapEnumerator<T, U = T> implements IEnumerator<U> {
+    private _enumerator;
+    private _map;
+    private _current;
+    private _index;
+    get current(): U;
+    constructor(enumerator: IEnumerator<T>, map: Morphism<T, U>);
+    toIterator<U>(): Iterator<U>;
+    moveNext(): boolean;
+    reset(): void;
+}
+export declare class TakeEnumerator<T> extends HelperEnumerator<T> {
+    private _limit;
+    constructor(enumerator: IEnumerator<T>, limit: number);
+    moveNext(): boolean;
+}
+export declare class FusedEnumerator<T> implements IEnumerator<T> {
+    private _enumerators;
+    private _index;
+    get current(): Nullable<T>;
+    constructor(enumerators: IEnumerator<T>[]);
+    private _cur;
+    private _done;
+    toIterator<T>(): Iterator<T>;
+    moveNext(): boolean;
+    reset(): void;
+}
+export declare class Enumerable<T> implements IEnumerable<T>, Iterable<T> {
+    protected _enumerator: IEnumerator<T>;
+    constructor(enumerator: IEnumerator<T>);
+    static from<T>(value: IEnumerable<T> | IEnumerator<T> | Iterable<T> | Iterator<T>): Enumerable<T>;
+    static isEnumerable<T>(value: object): value is Enumerable<T>;
+    static isEnumerator<T>(value: object): value is IEnumerator<T>;
+    [Symbol.iterator](): Iterator<T>;
+    at(index: number): Nullable<T>;
+    atOrDefault(index: number, defaultValue: T): T;
+    atOrElse(index: number, defaultValue: () => T): T;
+    concat(other: IEnumerable<T>): IEnumerable<T>;
+    drop(limit: number): Enumerable<T>;
+    enumerator(): IEnumerator<T>;
+    every(predicate: Predicate<T>): boolean;
+    filter(predicate: Predicate<T>): IEnumerable<T>;
+    flatMap<U>(fn: Morphism<T, IEnumerator<U>>): IEnumerable<U>;
+    map<U>(fn: Morphism<T, U>): IEnumerable<U>;
+    some(predicate: Predicate<T>): boolean;
+    take(limit: number): IEnumerable<T>;
+}
+export declare class ArrayEnumerble<T> extends Enumerable<T> {
+    at(index: number): Nullable<T>;
+}
+export {};