Function to calculate the nth Fibonacci number using the closed form. It uses the Ring Z(sqrt 5) so it can use arbritary precision arithmetic.
This function was created as exercise and I wouldn't use it in production, it also was never intended to be installed.
This implementation was discussed in https://codereview.stackexchange.com/questions/241541/closed-form-fibonacci-using-integer
I use stack. It builds with
stack build
I run it via stack exec -- fibonacci-exe 123 - where 123 is a placeholder for the nth Fibonacci number.