typing-operators.ts

// ------- Typing Operators -------
// https://github.com/pirix-gh/medium/blob/master/types-curry-ramda/src/index.ts

export type Iterator<
  Index extends number = 0,
  From extends any[] = [],
  I extends any[] = []
> = {
  0: Iterator<Index, Next<From>, Next<I>>;
  1: From;
}[Pos<I> extends Index ? 1 : 0];

export type Length<T extends any[]> = T["length"];
export type Prepend<E, T extends any[]> = ((
  head: E,
  ...args: T
) => any) extends (...args: infer U) => any
  ? U
  : T;
export type Pos<I extends any[]> = Length<I>;

export type Reverse<
  T extends any[],
  R extends any[] = [],
  I extends any[] = []
> = {
  0: Reverse<T, Prepend<T[Pos<I>], R>, Next<I>>;
  1: R;
}[Pos<I> extends Length<T> ? 1 : 0];

export type Concat<T1 extends any[], T2 extends any[]> = Reverse<
  Reverse<T1> extends infer R ? Cast<R, any[]> : never,
  T2
>;

export type Next<I extends any[]> = Prepend<any, I>;

export type Cast<X, Y> = X extends Y ? X : Y;

export type Append<E, T extends any[]> = Concat<T, [E]>;

// End of Typing Operators------