From: "Mauricio Fernández" <batsman.geo@...>
Date: 2002-08-23T01:45:37+09:00
Subject: Re: Puzzeled by Range object

On Thu, Aug 22, 2002 at 05:08:59PM +0900, Peter Hickman wrote:
> However you might write come code such as
> 
> (start..10).each {|x| ... }
> 
> I would expect such code to loop from start to 10 for a values of start 
> <= 10. For values greater than 10 I would not expect the code to run.
> 
> For my code to start 'running backwards' as it were would be very 
> counter intuative.

Then I'll give another name for the new iterator with the other
semantic. Plus now "reverse" ranges are processed in order,
ie 1..-3 => 1 0 -1 -2 -3  instead of -3 -2 -1 0 1 as before.

Note that when doing (A..B).each2, 
 A.succ must be defined if A < B
 B.succ must be defined if B >= A
That's why (1..2.3).each2 and (1.1..-3).each2 both work
but not (1.1..3).each2 nor (1..-3.1).each2.

A <=> B (or the reverse) must be defined in both cases.


batsman@kodos:~/src/rubylang$ cat myrange.rb


class Range
 def each2
	if (first <=> last) == -1
		# proceed in normal order
		a = first
		while (a <=> last) == -1
			yield a
			a = a.succ
		end
		yield last unless exclude_end? if (a <=> last) == 0
	else
		# reverse!
		v = []
		a = last
		a = a.succ if exclude_end?
		while (a <=> first) == -1
			v << a
			a = a.succ
		end
		v << a if (a <=> first) == 0
		v.reverse!
		v.each { |x| yield x }
	end
 end
end

l = [	"(1..3).each2 { |x| print x, ' ' }",
	"(1..-3).each2 { |x| print x, ' ' }",
	"(1...3).each2 { |x| print x, ' ' }",
	"(1...-3).each2 { |x| print x, ' ' }",
	"(1..3.1).each2 { |x| print x, ' ' }",
	"(1...3.1).each2 { |x| print x, ' ' }",
	"(1.1..-3).each2 { |x| print x, ' ' }",
	"(1.1...-3).each2 { |x| print x, ' ' }",
]

l.each { |x| print "Executing #{x}: "; eval x; puts }

batsman@kodos:~/src/rubylang$ ruby myrange.rb
Executing (1..3).each2 { |x| print x, ' ' }: 1 2 3
Executing (1..-3).each2 { |x| print x, ' ' }: 1 0 -1 -2 -3
Executing (1...3).each2 { |x| print x, ' ' }: 1 2
Executing (1...-3).each2 { |x| print x, ' ' }: 1 0 -1 -2
Executing (1..3.1).each2 { |x| print x, ' ' }: 1 2 3
Executing (1...3.1).each2 { |x| print x, ' ' }: 1 2 3
Executing (1.1..-3).each2 { |x| print x, ' ' }: 1 0 -1 -2 -3
Executing (1.1...-3).each2 { |x| print x, ' ' }: 1 0 -1 -2
batsman@kodos:~/src/rubylang$



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