02-assign-and-define.bc

# phi is a constant
let phi = (1 + sqrt(5)) / 2

# fib(n) calculates the nth Fibonacci number based on Binet's formula.
define fib(n) {
  let psi = 1 - phi
  return (phi ^ n - psi ^ n) / (phi - psi)
}

fib(1)
# == 1

fib(3)
# == 2

fib(10)
# == 55