On Tue, 6 Jun 2023 john o goyo wrote:
I have always regarded the definition module as the file that defines
the interface to the module.
I have thought of that myself, but it doesn't really help because if we apply the same logic to implementation modules, they would be definition modules, too since they *define* the implementation.
I was curious about the origin of the term and suspected that it wasn't Wirth who came up with it, because he didn't design Modula-2. Xerox did.
And indeed, the terminology does go back to Xerox PARC.
The Mesa Language manual (Version 5.0) states on page 101:
"An interface is a connector between programs: it allows code in one module to access parts of other modules, specifically procedures, signals and variables. Interfaces are _defined_ by definitions modules."
However, it then immediately continues:
"They contain _declarations_ for public items ..."
It boggles the mind. It's not even a naive mistake that crept in due to somebody mixing up definition and declaration. It clearly shows they knew that they were using incorrect and counterproductive terminology. It smacks of one of those cold war "Just to confuse the Russians" things.
So the blame goes to Lampson, Mitchell, Satterwhite, Geschke and Sweet at Xerox. Although, as a university professor, Wirth could and should have spotted this folly and corrected it when he gave Mesa a Pascalian syntax facelift that resulted in Modula-2. A very unfortunate missed opportunity.
To their credit, many of the people who worked on Mesa at Xerox PARC later went to DEC's Research Center where they then worked on DEC's Modula-2+ and Modula-3 languages and corrected their erstwhile mistake by changing terminology and syntax to _interface_ module.
I am a great believer in the single syntax principle and thus not a friend of synonym symbols, but this whole thing tempts me to add INTERFACE as a synonym for DEFINITION to my compiler. If even the guys who messed this up corrected their own mistake, it seems silly not to follow their example.
Anyway, thanks for the feedback.
regards
benjamin