sidef/scripts/functional_summation_of_fractions.sf

#!/usr/bin/ruby

#
## Rational summation of fractions
#

var k = 0       # initial value of the counter

func a(n) { (-1)**n }       # numerator
func b(n) { 2*n + 1 }       # denominator

func g((k))         { b(k) }
func g(n) is cached { b(n) * g(n-1) }

func f((k))         { a(k) }
func f(n) is cached { b(n)*f(n-1) + a(n)*g(n-1) }

for i in (k .. 10) {
    say [f(i), g(i)]
}