GheorgheP

type Null = undefined | null
type MVal<T> = T | Null
type Nullify<T> =  {
    [P in keyof T]: MVal<T[P]>;
};
type MParams<T extends (...args: any) => any> = T extends (...args: infer P) => any ? Nullify<P> : never;

declare function apply<F extends (...args: any) => any>(f:F, ...args: Parameters<F>): ReturnType<F>

declare function mApply<F extends (...args: any) => any>(f:F, ...args: MParams<F>): MVal<ReturnType<F>>

GheorgheP

type Null = undefined | null
type MVal<T> = T | Null

declare function mFn<T, R>(f:(a:T) => R): {
  (a: T): R,
  (a: Null): Null
}

declare function mFn<T, T2, R>(f:(a:T, b:T2) => R): {
  (a: T, b:T2): R,

GheorgheP

const composeAsync = (...fs) => {
  if (fs.length === 0) {
    throw new Error('compose requires at least one argument')
  }

  return async (...as) => {
    const call = async fs => {
      const f = fs[0]
      const tail = fs.slice(1, Infinity)
      return await tail.length === 0 ? f(...as) : f(await call(tail))

GheorgheP

const curry = f => {
  const _curry = (args = []) => args.length < f.length ? (...a) => _curry([...args, ...a]) : f(...args)
  return _curry()
}