On Fri, Feb 16, 2007 at 12:07:43PM -0800, Steve Lukas wrote:
: Larry, Smylers, now I've read your answers.
: Larry, thanks for telling me that it is already specced.
: I have overlooked it, sorry.
: Hello Smylers, thanks for your answer, too. I'm not stucked on
: the form C<$-name>. I am happy to get the runtime readonly
: or the pragma.
The "is readonly" is part of the declaration, and can therefore give you
compile-time diagnostics as well as run-time. The run-time check is
merely a fail-safe for situations where the compiler can't determine
that you're attempting to modify something.
That being said, in writing the Perl 6 grammar I keep running into the
need for rw context variables. I'm getting tired of writing things like:
my @heredoc_stubs is context is rw = ()
so maybe there's some general syntactic relief for rw/ro that is
orthogonal to everything else. But that means it wouldn't be a
trait, a type, a sigil, or a twigil, if it's really orthogonal.
I don't just want to go with bare rw and ro markers because I think
they're too easy to confuse. It's more like we want an initializer
that says "lock this after I change it". If used on the initializer
of a declaration it would have the force of a readonly declaration.
Some variant on or near the =, in other words, that could also be
a variant on normal assignment. But maybe it also has to
stand alone to declare it as a "write once" variable, I expect.
Currently "is readonly" only works on the declaration, and only on
items that are initialized by the declaration. Maybe that's good
enough for most purposes.
This isn't quite what context variables want though. They tend to
want to be writeable in the current scope and then either ro or rw
in sub-scopes. So I've been wondering whether we should split the "is
context" declarator into two, one of which is for passing immutable
info downward like environment variables, and one of which is for
passing data upward to a mutable target, kinda like the implicit target
of a gather. Don't know what the syntax for that should be though.
Unfortunately the opposite of "context" is not "pretext", though that's
kind of a funny pun--set this variable up ahead of time to gather
text. And "protext" isn't a word, that I know of...
I guess I need to visit the thesaurus for all the words that mean
disseminate and assemble...
Other ideas will be gladly entertained before being rejected. :-)
Larry
