On Mon, Jan 20, 2014 at 11:12 PM, spir <denis.spir@gmail.com> wrote:
> For instance, closed intervals are more intuitive or natural, obviously (but
> for some reason I don't know). If you ask someone to count from 1 to 9, you
> will probably be surprised to hear him/her start from 2 or stop after 8. If
> you are asked to choose a letter between c and g, you will probably be
> surprised to hear that 'c' or 'g' is no good choice.

I'm not so sure about that. The half-open interval makes as much sense
as the fully closed - all you have to do is interpret the indices as
being *between* elements. Take, for example, Scripture verses. (Quotes
taken from THE HOLY BIBLE, NEW INTERNATIONAL VERSION®, NIV® Copyright
© 1973, 1978, 1984, 2011 by Biblica, Inc.® Used by permission. All
rights reserved worldwide. Copyright notice included for license
compliance. Note that I'm using bracketed numbers to indicate the
beginnings of verses - in a printed Bible, these would normally be in
superscript.)

John 14:
[31] To the Jews who had believed him, Jesus said, “If you hold to my
teaching, you are really my disciples. [32] Then you will know the
truth, and the truth will set you free.” [33]

This passage is normally referred to as "John 14:31-32", but as you
see, the verse marker [32] is in the middle of the quote. Using a
half-open interval, this would start at "John 14:31" and end at "John
14:33". Half-open means: "Begin at the beginning, go on till you come
to the end, then stop", as the King of Hearts instructed the White
Rabbit.

It's easy to indicate the beginning of a chapter: your start reference
is verse 1. Here's the beginning of the account of the creation of the
world:

[1] In the beginning God created the heavens and the earth. [2] Now
the earth was formless and empty, darkness was over the surface of the
deep, and the Spirit of God was hovering over the waters. [3] And God
said, “Let there be light,” and there was light. [4] God saw that the
light was good, and he separated the light from the darkness. [5] God
called the light “day,” and the darkness he called “night.” And there
was evening, and there was morning—the first day. [6]

Common parlance: Genesis 1:1-5. Half-open: Genesis 1:1-6. Conclusion:
Tie. No argument to be made for either side. But what if you're
looking at the *end* of a chapter? Here are a few verses from later on
in Genesis 1:

[29] Then God said, “I give you every seed-bearing plant on the face
of the whole earth and every tree that has fruit with seed in it. They
will be yours for food. [30] And to all the beasts of the earth and
all the birds of the air and all the creatures that move on the
ground—everything that has the breath of life in it—I give every green
plant for food.” And it was so. [31] God saw all that he had made, and
it was very good. And there was evening, and there was morning—the
sixth day.

Common parlance: Genesis 1:29-31. Half-open: Genesis 1:29-2:1. It's
much more obvious by the latter that this passage extends exactly to
the end of the chapter.

Obviously it's way WAY too late to change the way Bible references are
written, any more than Melway could renumber their maps all of a
sudden. Massive case of lock-in and backward-incompatibility with
existing code. But I put it to you that the half-open would make at
least as much sense as the closed, in any situation where there are
boundaries with contents between them.

Note, by the way, that I'm not looking at anything involving backward
scanning or wider strides, both of which Python's slice notation
supports. Neither of those is inherently real-world intuitive, so the
exact semantics can be defined as whatever makes sense in code. (And
there was some discussion a little while ago about exactly that.) I'm
just looking at the very simple and common case of referencing a
subset of consecutive elements from a much larger whole.

The closed interval makes more sense when the indices somehow *are*
the values being retrieved. When you count from 1 to 9, you expect
nine numbers: 1, 2, ..., 8, 9. When you list odd numbers from 1 to 9,
you expect 1, 3, 5, 7, 9. But what if you're looking at a container
train and numbering the twenty-foot-equivalent-units (TEU) that it
has? A 40-foot container requires 2 TEU, a 60-foot container requires
3 TEU. A "reefer" (refridgerated container) might require an extra
slot, or at least it might be a 56-footer and consume 3 TEU. One wagon
might, if you're lucky, carry 5 TEU; numbering them 1 through 5 would
be obvious, but numbering the boundaries between them as 0 through 5
is better at handling the multiple TEU containers. (Even more so when
you look at double-stacked containers. An over-height 40-foot
container could consume 2 TEU horizontally and 2 TEU vertically, and
be put in slots (0,0)-(2,2). This is, in fact, exactly how a GTK2
Table layout works.) Both types of intervals have their places.

ChrisA

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