Re: Beginner's Language?

[thornley@visi.com (David Thornley)]

In article <3B166490.98133E58@ftw.rsc.raytheon.com>,
Wes Groleau  <wwgrol@ftw.rsc.raytheon.com> wrote:
>
>> P.S.  Any language where you can add two positive numbers together and get a
>> negative number is inherently broken.  It is a sign of the language designer
>> and compiler writer choosing their own convenience over yours.
>
>Since Java was not one of the many newsgroups posted to,
>I presume it is not the only language with such a stupid
>feature?
>
It's fairly usual in C.  The C standard leaves the case of
arithmetic overflow in signed types undefined, which means
that the result could be negative, imaginary, text, or armed
with thermonuclear weapons for all the standards care.
Most systems I've used it on will wrap around, so that adding
positive numbers and overflowing the limits will give you
a negative number.

Partly the choice of languages depends on such things as
whether you wish to get the right answer almost immediately
or the wrong one with even greater speed.  I never want
to have to trust intermediate results not to overflow,
which is one of the many reasons I like Common Lisp (in 
which case such overflow yields the right answer at a loss
in speed).

Other interesting behaviors are truncation on the left because
somebody left a 9 off a variable definition in COBOL.  I've
seen that cost thousands of dollars (well, to be honest, the
client being billed probably saw it as a savings of thousands
of dollars).  I've heard of such behavior in PL/I, a language
I have never had the pleasure of working in.

You can also avoid some floating-point errors in Common Lisp
by using rational numbers instead of floating-point.  (/ 1 3)
evaluates to an honest 1/3 rather than a floating-point
approximation.  If (+ (/ 1 3) (/1 3) (/1 3)) doesn't yield
1, your CL system has problems.  Pity about transcendental
functions that have rational values on only a few points of
their range.

--
David H. Thornley                        | If you want my opinion, ask.
david@thornley.net                       | If you don't, flee.
http://www.thornley.net/~thornley/david/ | O-