"use strict";

// head :: Array a → a
const head = ([head, ...tail]) => head;
// tail :: Array a → Array a
const tail = ([head, ...tail]) => tail;

// unique :: Array Number → Array Number
const unique = ( ls, acc = [] ) => {
  if ( ls.length === 0)  return acc;
  if ( acc.indexOf( head( ls ) ) == -1 ) return unique( tail( ls ), acc.concat( head( ls ) ) );
  return unique( tail( ls ), acc );
}

const nums = [1,2,5,7,4,0,33,48,3,8,4,569,0,23,4,1,9];

console.log(
  unique(nums)
)