Simple partial application with placeholders, example for discussion

example-partial-application-with-placeholders.js

export class Placeholder {}
export const _ = new Placeholder()
export const isPlaceholder = placeholder => placeholder instanceof Placeholder

export function bind( ...placeholders ) {
  return ( ...fillers ) => this.call( this, ...placeholders.map(
    item => isPlaceholder( item ) ? fillers.shift() : item
  ) )
}