Re: Clause "with and use"

["Robert I. Eachus" <rieachus@comcast.net>]

Dmitry A. Kazakov wrote:

> Does anybody a statistics of name clashes in Ada?

Let me tell you a funny story about that.  Right after Ada became an 
ANSI standard in 1983, I was talking to Dan Eilers and Jean Ichbiah in 
the Irvine Compiler suite at a SIGAda meeting in San Diego.  Jean had 
asked what I thought of the new standard--I had a copy with me, and this 
was fairly early days, February 1983.

I said that there was one change from the Printer's Proof edition that 
troubled me.  Name and System_Name in System had been reversed, making 
Name the type and System_Name a constant.  I said I had considered a 
recommendation that Name become a function instead of a constant, so it 
could be overloaded, but that this was much worse.

"Why?" Ichbiah asked.

"Well, Name is going to occur often as a function name, in fact there is 
a function Name in Text_IO.  This creates a surprising "Gotcha!" that 
there was no real need for."

"Never happen in a million years," Ichbiah replied.  "That would require 
a program to have use clauses for both Text_IO and System, and then try 
to get the name of a file."

A few minutes later Robert Dewar came over and interrupted.  "Dan, I 
think I found a bug in your compiler.  I wrote a little test program, 
and it won't let me call Name in Text_IO.  Says it isn't visible."

"Do you have a use clause for Text_IO?" I asked.

"Of course," said Robert Dewar looking puzzled.

"And a use clause for System?"

"As a matter of fact, yes," Robert said, and then looked on in 
astonishment and Dan and I burst out laughing.

I had to explain that the joke wasn't on him, but on Jean Ichbiah, and 
that little glitch was in the language for good.  (In case you are 
wondering, it is still in the language twenty years later.)  Has it 
bitten anyone else in the twenty years since?  Probably.  This is just 
one reason why the ARG is careful to fully examine ALL the consequences 
of a langauge change.

-- 
                                           Robert I. Eachus

100% Ada, no bugs--the only way to create software.