number ranges

[Paul Rubin]

aleaxit at yahoo.com (Alex Martelli) writes:
> > for i in (1 to 10 by 3):
> >      print i
> > 
> > should print 1 4 7.
> 
> But that would be an "attractive nuisance" to many other native speakers
> like you, who would instinctively think of a closed interval.  Maybe
> 'upto' rather than 'to', as somebody else suggested, would ease that.

I don't think "upto" is any better.  Any distinction that might exist
between "to" and "upto" doesn't jump out at me.

I notice that Haskell uses closed intervals: [1..5] means [1,2,3,4,5].
Is that an error by Haskell's designers?  One possibility is that those
intervals don't actually get used in ways likely to cause one-off errors.
I haven't used Haskell enough to have any sense of this.

Here's something ugly but explicit, somewhat Haskell-inspired:

   (1 .. )    # infinite generator, like Haskell
   (1 .. < 10)   # semi-closed interval: 1,2,3...,9
   (1 .. <= 10)  # closed interval: 1,2,3...,10
   (1,4 .. < 10)  # semi-closed: 1,4,7
   (1,4, .. <= 10)  # closed: 1,4,7,10

This would be horrible for Python though.