From: "Hal E. Fulton" <hal9000@...>
Date: 2002-09-11T03:54:33+09:00
Subject: Re: Larry Wall's comments on Ruby

----- Original Message -----
From: "nico" <n1k0@rogers.com>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Tuesday, September 10, 2002 9:31 AM
Subject: Re: Larry Wall's comments on Ruby


> On September 10, 2002 04:38 am, Gavin Sinclair wrote:
>
> > I'm not convinced that it's unnatural.  We don't know the types of a and
> > b, and for some objects a and b, a + b != b + a.
> >
> > I'm interested what you think the alternative is, or an argument against
> > the above, and how you would like to see a + b defined in Ruby.
> >
> > Gavin
>
> I find that highly unnatural because we've been learning since grade
school
> that a + b = b + a.
>
> If the objects don't satisfy that property they should be using a
different
> symbol.

True, but only up to a point. There's a boundary
between mathematics and programming languages,
and this pushes the boundary.

First of all, even "=" doesn't mean in Ruby
what we learned in grade school.

This makes sense in Ruby (as an imperative):
  x = x + 1
but in math, it's just a false statement
or an equation with no solution.

Also, math doesn't distinguish between integers
and reals in the same way. (Yes, it DOES have
the concept, but it's not the same as in Ruby.)
A Float in Ruby is a finite subset of the rational
numbers which are an infinite subset of the real
numbers.

In math, if I say 5 + 3.2, I don't worry that
the numbers are different "types." I mentally
promote the 5 to 5.0 and go on and get 8.2.

But in Ruby, these are actually different types
(different classes). It's not *entirely* obvious
what should happen.

You *could* argue that an integer plus a float
should "demote" the float: 5 + 3.2 yields 8.

After all, aren't we used to this in division?
We often make the useful definition that 10/3
yields an integer while 10/3.0 yields a float.

Bottom line: The analogy between math and a
programming notation is imperfect.

Hal