On Tue, 10 Oct 2000, Brian Goetz wrote:
>
> >#foreach $element in $list $element #end
> > 1 2 3 4
> >
> >If all directives are pluggable then there
> >is nothing specific in the grammar to
> >catch a #foreach $element in $list. You are basically
> >looking for #anything, then a list of arguments.
> >In the above example it's not possible to tell
> >that (4) is in the body of the #foreach without
> >giving the parser a hint i.e. the number of
> >arguments to the directive. So a #foreach has
> >three arguments so what follows must be the
> >body of loop.
>
> Actually, what I did in WM is a little more complicated, but this is
> close. Each directive has a directive descriptor, which includes a list of
> argument descriptors. Argument descriptors describe an argument, and there
> are defined types for Conditional, LValue, RValue, Keyword, Block, etc. So
> the argument list for #foreach would be: ( LValue, Keyword("in"), RValue,
> Block )
>
> While this solves the problem of backward compatibility in WM, it does make
> the parser more complicated. Jason's idea of delimiting the argument list
> with ( .. ) seems to work, although you're still going to want to be able
> to say that some directives require a block (like #if and #foreach) and
> some don't (like #set.) I think this will still require some, but fewer,
> JAVACODE productions.
You still have to know whether the directive has blocks, yes, but we
have no JAVACODE productions and everything is working
fine. Geir and I are just finishing what we hope will be the
first production quality parser.
jvz.
