Fun with lazy sequences in Ruby and Python.

Defines a class Seq which allows one to do things like this:

fib = Seq.new(0, 1) { fib.rest + fib }
puts "Fibonacci numbers: #{fib.take 10} ..."

primes = Seq.up_from(2).select do |n|
  n < 4 or primes.take_while { |m| m * m <= n }.forall { |m| n % m > 0}
end
puts "Prime numbers: #{primes.take 10} ..."

or in Python:

fib = Seq(0, 1, lambda : fib.rest + fib)
print "Fibonacci numbers: ", fib.take(10), "..."

primes = Seq.up_from(2).select(
    lambda n: n < 4 or (primes.take_while(lambda m: m * m <= n).
                        forall(lambda m: n % m)))
print "Prime numbers:", primes.take(10), "..."

and finally in Coffeescript:

fib = seq.build 0, 1, -> fib.rest().add fib
console.log "Fibonacci numbers: #{fib.take 10} ..."

primes = seq.upFrom(2).select (n) ->
  n < 4 or primes.takeWhile((m) -> m * m <= n).forall((m) -> n % m > 0)
console.log "Prime numbers: #{primes.take 10} ..."