proper fibs

fb.hs

let fib n = 
        let phi = (1 + sqrt 5)/2 in 
        floor (((phi^n) - ((1-phi)^n)) / (sqrt 5))

fib.rb

#!/usr/bin/env ruby 
module Math
  PHI = (1 + Math.sqrt(5)) / 2
end
 
def fib n
  (((Math::PHI ** n) - ((1 - Math::PHI) ** n) ) / Math.sqrt(5)).to_i
end

if __FILE__ == $0
  puts fib(ARGV[0].to_i)
end