From: Robert Dober <robert.dober@...>
Date: 2007-06-08T04:41:32+09:00
Subject: Re: What about a 'series' type?

On 6/7/07, Robert Klemme <shortcutter@googlemail.com> wrote:
> On 07.06.2007 16:52, Peter Marsh wrote:
> >> primes = Series.new(Starting_value,Some_block_to_define_serires)
> >
> > Just wanted to be a bit clearer about this, the second argument is a
> > block which can generate nth term in a series. This would probally take
> > a while for primes, but if it were recursive then it would be easier...
>
> IMHO for a series it would be more natural to let the block calculate
> a[n+1] from a[n] wouldn't it?  Of course, for Fibonacci this would only
> work if you allow for multiple arguments.
>
> Something like
>
> #!ruby
> class Serial
>    include Enumerable
>
>    def initialize(*init, &f)
>      @init = init
>      @f = f
>    end
>
>    def each(&b)
>      a = b.arity
>      current = @init
>      loop do
>        b[*current[0 ... a]]
>        current = Array(@f[*current])
>      end
>      self
>    end
> end
>
> s1 = Serial.new 0 do |x| x+1 end
> s1.each {|x| p x; break if x > 10}
>
> puts
>
> s2 = Serial.new 0,1 do |a,b| [b,a+b] end
> s2.each {|x| p x; break if x > 40}
>

Robert I hope you do not mind my fantasy about/over/at??? your theme.

class Serial
  include Enumerable

  def initialize(*init, &f)
    @init = init
    @f = f
    @arity = f.arity
  end

  def get_some( some = nil, &b)
    @current = @init.dup
    if some && b.nil? then
      (0...some).inject([]) do |acc,|
        compute_next
        acc << @current.first
      end
    else
      a = b.arity
      loop do
        break if some && ( some -= 1 ) < 0
        b[*@current.first( a )]
        compute_next
      end
      self
    end
  end

  private
  def compute_next
    @current += Array( @f[*@current] )
    @current = @current.last @arity
  end
end

s1 = Serial.new 0 do |x| x+1 end
s1.get_some {|x| p x; break if x > 10}
puts "-"*42
puts s1.get_some(6)

puts "-"*42
f = Serial.new 1, 1 do |x, y| x + y end
f.get_some(6){ |x,| puts x }

puts "-"*42
a = Serial.new 1, 1, 1 do |x, y, z| x + y + z end
puts a.get_some(6)

Cheers
Robert



-- 
You see things; and you say Why?
But I dream things that never were; and I say Why not?
-- George Bernard Shaw