[Types-sig] Re: Pascal style declarations

[Golden, Howard]

Greg Stein [mailto:gstein@lyra.org] wrote:

> You don't provide a way to declare function return value(s) 
> types. When
> you do, then I think you're going to run into a problem using the ':'
> syntactical marker...

[refers to:]

> > 3.  In functions and methods, you can _optionally_ specify 
> the argument
> > type:
> > 
> >     def funx(x : int, y : string): ...
> > 

I'll admit that Python already uses the ":" character where Pascal does, but
so what?  You can still specify the return type in other ways.  The most
obvious (to me) is to use the ":" character twice, e.g.,

    def funx(x : int, y : string): int : ...

While I'm not a parsing expert, I believe this would still be parsable.  Of
course, any other available character could be used instead of the ":", if
this would be preferable.  (Again, I'm not trying to dictate the final
syntax, just suggest a starting point.)

> This was one reason that Fred/Sjoerd/myself moved away from ':'-based
> declarations, and eventually fell into expression-based type checking.

I am suggesting using declarations, rather than expression-based type
checking, since that is familiar in other languages.  As a declaration, it
is clear that I am talking about an invariant assertion, not a dynamic one.

Expression-based type checking should also be available, since it is needed
when static checking is impossible.  I don't think it has to be either/or.