Perl6: What is "idfirst letter"?

[rir]

Quoting Synopsis 2:

The $Package'var syntax is gone. Use $Package::var instead. (Note, however, that identifiers may now contain an apostrophe or hyphen if followed by an "idfirst" letter.)

This seems to be the only occurance in the Synopses of the term "idfirst". What is it and is it current?

Be well,
rir

[moritz]

Thanks for the question, I've tried to clarify it.

I think "idfirst" meant "a character that is allowed as the first character of an identifier", and the authoritative source in all parsing questions says that's <.alpha> (Unicode category "Letter", or the underscore).

[ikegami]

Well, in Perl5, "[" and U+0001 are allowed as the first (and only) character of an identifier, but I don't think anyone would consider them idfirst. I don't know if Perl6 has such exceptions.

[moritz]

No. There are special variables with "weird" names ($/, $!, $¢) but they aren't identifiers.

I also don't think that [ counts as an identifier character in Perl 5, because you can't write sub [ { }

[ikegami]

Identifiers are usually of the form

identifier: idfirst idcont*

For example, identifiers can usually contain digits, but not in the first position.

It sounds like Perl6 will allow

identifier: idfirst idcont* ( [-'] idfirst idcont* )*

What is it and is it current?

Actually, identifiers aren't well defined in Perl5. Tom Christiansen tried to hammer down the definition on p5p in the last two weeks, but I didn't follow the conversation. I'll locate it if you ask.

[tchrist]

“idfirst” is jut an abbreviation for any code point with the Unicode ID_Start property.

Anyway, Perl identifiers don’t seem to pay as much attention to IDS as you would think. You can start them with other types of decimal numbers and connector punctuation, both of which are IDC (ID_Continue) not IDS.

[Anonymous Monk]

I guess it is like [a-zA-Z] in perl5, has to be first letter of subroutine name sub a4567, except perl6 equivalent (probably similar)

[ikegami]

The set is much much larger than that in Perl5. For example, identifiers can start with "_" and "é".