From: William James <w_a_x_man@...>
Date: 2005-09-20T16:51:38+09:00
Subject: Re: ruby idiom for python's for/else while/else

Brian Mitchell wrote:
> On 9/19/05, Jeremy Tregunna <jtregunna@blurgle.ca> wrote:
> >
> > On 19-Sep-05, at 7:15 PM, Gergely Kontra wrote:
> >
> > > Hi!
> > >
> > > Is there a similar construct to python's:
> > >
> > >>>> for n in range(2, 10):
> > > ...     for x in range(2, n):
> > > ...         if n % x == 0:
> > > ...             print n, 'equals', x, '*', n/x
> > > ...             break
> > > ...     else:
> > > ...         # loop fell through without finding a factor
> > > ...         print n, 'is a prime number'
> > > ...
> > > 2 is a prime number
> > > 3 is a prime number
> > > 4 equals 2 * 2
> > > 5 is a prime number
> > > 6 equals 2 * 3
> > > 7 is a prime number
> > > 8 equals 2 * 4
> > > 9 equals 3 * 3
> >
> > Directly, yes; though hardly anybody writes code this way (at least
> > I've never seen anybody write something like this, like how I'm about
> > to give it to you). I'd see William Morgan's message for a better
> > suggestion.
> >
>
> # I hate for loops
>
> 2.upto(10) do |n| # was => for n in (2..10) do
>     2.upto(n) do |x| # was => for x in (2..n) do
> >      if n % x == 0
> >        puts "#{n} equals #{x} * #{n/x}"
> >        break
> >      else
> >        puts "#{n} is a prime number"
> >      end
> >    end
> > end
> >
>
> Though, I think this is broken... check the output.
>
> > > Gergo
> >
> > --
> > Jeremy Tregunna
> > jtregunna@blurgle.ca
> >
> > "If debugging is the process of removing bugs, then programming must be
> > the process of putting them in." --Dykstra
> >
>
> I still think lists are the nicest way to go about this. It could be
> much improved but this is shorter:
> (2..10).select {|n| (2..n).select {|x| n % x == 0 and n != x }.empty? }
>
> Brian,

(2...50).select{|n|(2..Math.sqrt(n).to_i).select{|x|n % x == 0}.empty?}
     -->
[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47]