The Fibonacci sequence in Io

fibonacci_spec.io

Fibonacci := Object clone

Fibonacci generate := method(n,
  if(n == 1 or n == 2, 1, generate(n - 1) + generate(n - 2))
)

Object Fibonacci := Fibonacci

describe(fibonacci, Fibonacci,
  setup(
    f := Fibonacci clone
  )

  fibonacci(1, verify(Fibonacci generate(1) == 1))
  fibonacci(2, verify(Fibonacci generate(2) == 1))
  fibonacci(3, verify(Fibonacci generate(3) == 2))
  fibonacci(4, verify(Fibonacci generate(4) == 3))
  fibonacci(5, verify(Fibonacci generate(5) == 5))
  fibonacci(6, verify(Fibonacci generate(6) == 8))
  fibonacci(7, verify(Fibonacci generate(7) == 13))
)