[m-dev.] io__write et al
fjh at cs.mu.oz.au
Wed Apr 23 15:06:01 AEST 1997
Peter Schachte, you wrote:
> > > Shouldn't we start encouraging the notation `io:print'?
> > No. That notation should be DIScouraged, because it is going to change
> > to `io.print'. But of course we shouldn't start encouraging the notation
> > `io.print' until after we have implemented it...
> This doesn't seem like a good idea.
> What's the rationale for making this change?
The rationale is that this seems to be the best way of coming up with a simple,
consistent syntax for type qualification, module qualification, and records.
Module qualification: . module.name
Type qualification: : expr : type
:- type foo ---> foo(
field_name1 : type1,
field_name2 : type2
Mode qualification: :: :- pred p(type::mode).
I still haven't quite figured out what I think the best syntax is for all the
record operations, though.
> Firstly, it is error prone, as some
> people will tend to write io . print(...).
It may be a little confusing initially for some people, but I don't think
it will be error prone. I think people will just get into the habit of
writing `io.print'. I don't think this is the sort of mistake that any
given person would be likely to make often.
(Now comma as separator is error-prone...)
Anyway, if we are going to use dot as an operator despite this problem,
then module qualification is a good choice.
> Thirdly, does this mean that we can't use '.' as this list constructor
> anymore? Shouldn't io.print() be the list [io|print()]?
You can't use infix '.' as the list constructor, but that is not a change;
that is enshrined in ISO Prolog, and has always been the case in Mercury.
If you want to use '.' as the list constructor, you have to write it prefix.
> Secondly, the infix dot
> notation is more orthodoxly used for structure member reference,
True, but many languages use it for both structure members and module
> Finally, colon is a much more conventional module qualification operator.
Prolog is the only language I know that uses ":" as a module qualification
Language Modules Types Structs
-------- ------- ----- -------
Haskell module.member expr::type field record
Ada package.member var:type record.field
Java package.member class.member
SML structure.member expr:type record.field
C++ namespace::member class.member or
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