Fibonacci in JavaScript - Concatenative-style

0-Readme.md

Fibonacci Sequence in Javascript - Concatenative-style

Demo on how to produce the Fibonacci Sequence in Javascript - Concatenative-style.
Drawing inspiration from Concatenative Programming Languages, such as Forth and Factor,
this demonstration relies on recursion or iteration only for ease-of-use rather than functionality.

1-fib.js

const fib = ([a,b,...c]) => [a+b,a,b,...c] 

fib([1,0])                         // --> [1,1,0]
fib(fib(fib([1,0])))               // --> [3,2,1,1,0]

2-repeat.js

const repeat = (n, f, a) => {
    console.log(n,f,a)
    let x = f(a);                  // store returned value of applying args to function
    return (n - 1) == 0 ? x        // if we are at zero return x
	  : repeat(n - 1, f, x) ;  // else repeat again, this time decreasing counter by one
}

repeat(3,fib,[1,0])                // --> [3,2,1,1,0]

3-repeat-iter.js

// I'm 98% sure that the repeat above is tail call optimized,
// but most Javascript engines don't perform TCO,
// so here is an iterative version:

const repeat_iter = (n, f, a) => {
  let x = a
  for (let i = n; i > 0; i--) {
    x = f(x)
  }
  return x
}

repeat_iter(3,fib,[1,0])           // --> [3,2,1,1,0]