Partial, or total, mess

partial.ts

type _ = {
  partial: Partial
};

type Partial = {
  /* WITH PLACEHOLDERS */
  <T1, R> ( fn: FN<[T1], R>, a1: _ ): FN<[T1], R>,
  <T1, T2, R> ( fn: FN<[T1, T2], R>, a1: _ ): FN<[T1, T2], R>,
  <T1, T2, R> ( fn: FN<[T1, T2], R>, a1: _, a2: T2 ): FN<[T1], R>,
  <T1, T2, R> ( fn: FN<[T1, T2], R>, a1: T1, a2: _ ): FN<[T2], R>,
  <T1, T2, R> ( fn: FN<[T1, T2], R>, a1: _, a2: _ ): FN<[T1, T2], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: _ ): FN<[T1, T2, T3], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: _, a2: T2 ): FN<[T1, T3], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: T1, a2: _ ): FN<[T2, T3], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: _, a2: _ ): FN<[T1, T2, T3], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: _, a2: T2, a3: T3 ): FN<[T1], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: T1, a2: _, a3: T3 ): FN<[T2], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: T1, a2: T2, a3: _ ): FN<[T3], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: _, a2: _, a3: T3 ): FN<[T1, T2], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: _, a2: T2, a3: _ ): FN<[T1, T3], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: T1, a2: _, a3: _ ): FN<[T2, T3], R>,
  <T1, T2, T3, R> ( fn: FN<[T1, T2, T3], R>, a1: _, a2: _, a3: _ ): FN<[T1, T2, T3], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _ ): FN<[T1, T2, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2 ): FN<[T1, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: _ ): FN<[T2, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _ ): FN<[T1, T2, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2, a3: T3 ): FN<[T1, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: _, a3: T3 ): FN<[T2, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: T2, a3: _ ): FN<[T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: T3 ): FN<[T1, T2, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2, a3: _ ): FN<[T1, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: _, a3: _ ): FN<[T2, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: _ ): FN<[T1, T2, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2, a3: T3, a4: T4 ): FN<[T1], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: _, a3: T3, a4: T4 ): FN<[T2], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: T2, a3: _, a4: T4 ): FN<[T3], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: T2, a3: T3, a4: _ ): FN<[T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: T3, a4: T4 ): FN<[T1, T2], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2, a3: _, a4: T4 ): FN<[T1, T3], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2, a3: T3, a4: _ ): FN<[T1, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: _, a4: T4 ): FN<[T1, T2, T3], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: T3, a4: _ ): FN<[T1, T2, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2, a3: _, a4: _ ): FN<[T1, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: _, a3: _, a4: T4 ): FN<[T2, T3], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: _, a3: T3, a4: _ ): FN<[T2, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: T2, a3: _, a4: _ ): FN<[T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: T1, a2: _, a3: _, a4: _ ): FN<[T2, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: T2, a3: _, a4: _ ): FN<[T1, T3, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: T3, a4: _ ): FN<[T1, T2, T4], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: _, a4: T4 ): FN<[T1, T2, T3], R>,
  <T1, T2, T3, T4, R> ( fn: FN<[T1, T2, T3, T4], R>, a1: _, a2: _, a3: _, a4: _ ): FN<[T1, T2, T3, T4], R>,
  /* WITHOUT PLACEHOLDERS */
  <HeadArgs extends any[], TailArgs extends any[], Return> ( fn: ( ...args: [...HeadArgs, ...TailArgs] ) => Return, ...headArgs: HeadArgs ): ( ...tailArgs: TailArgs ) => Return,
};