Special variable $¢ (Cursor) is not documented

[samcv]

Only https://design.perl6.org/S05.html mentions it.

[fluca1978]

Uhm..it also states that the match object and the cursor start the same in the beginning of the closure, but apparently I'm not able to get it:

> '123' ~~ / (\d) { say $0; say $¢; } \d+ /;
｢1｣
Nil

Also I'm not sure if such variable has to be documented at all, since it seems to me a little too much "magical" and the documentation for the Cursor states:
A user-space program usually doesn't need to deal with Cursor objects, just with their relatives, Match objects.

[JJ]

They might be useful in Grammars, for instance. So it might be necessary to document them, at least. However, it might also be necessary to find now what they actually do in the current implementation.

[JJ]

It does not seem to move:

 '123' ~~ / (\d) { say $/; say $¢; } (\d+) { say $/; say $¢; }/;

yields

｢1｣
 0 => ｢1｣
Nil
｢123｣
 0 => ｢1｣
 1 => ｢23｣
Nil

Is it maybe a not-yet-implemented feature?

[JJ]

In fact, Cursor is initalized like Match: https://github.com/rakudo/rakudo/blob/b07e7b1d0ffcafc1f9dfbb3d56eff59c8eaddbf8/src/core/Cursor.pm#L1
Nothing else. Looks to me NYI

[JJ]

Or maybe even won't be implemented; https://github.com/rakudo/rakudo/blame/b07e7b1d0ffcafc1f9dfbb3d56eff59c8eaddbf8/src/core/Cursor.pm#L1
The commit line talks about "Cursor/Match unification"

[samcv]

Hmm. Maybe this means that it should be removed or a deprecation warning added and then removed? If it's not documented/used anywhere.

[coke]

This variable does appear in a 6.c-errata test file.

[JJ]

Behavior now is different, BTW:

 m:  '123' ~~ / (\d) { say "» / »", $/; say "» ¢ »", $¢; } (\d+) { say  "» / »", $/; say  "» ¢ »", $¢; }/;  
 jmerelo, rakudo-moar a71e370bb: OUTPUT: «» / »｢1｣␤ 0 => ｢1｣␤» ¢ »｢1｣␤ 0 => ｢1｣␤» / »｢123｣␤ 0 => ｢1｣␤ 1 => ｢23｣␤» ¢ »｢123｣␤ 0 =>  ｢1｣␤ 1 => ｢23｣␤»

[AlexDaniel]

Are we all satisfied with the docs? I thought $¢ is now identical to just $/ after TimToady++'s recursor work. Am I wrong? Also, didn't we have a plan to remove $¢?

[JJ]

No, it's not the same as $/. Outside the regex, $/ contains the match object, $¢ is nil. Can add that to the documentation if needed.