From @zoffixznet

This .map multi in Backtrace.pm never gets acccessed​: https://github.com/rakudo/rakudo/blob/553cedb679f0f191d2f7341e05033505cb20ac7a/src/core/Backtrace.pm#L282

  <Zoffix> m​: Backtrace.new.map​: {...}
  <camelia> rakudo-moar 553ced​: OUTPUT«Ambiguous call to 'map'; these signatures all match​:␤​:(\SELF​: █; :$label, :$item, *%_)␤​:(Backtrace​:D $​: $block, *%_)␤ in block <unit> at <tmp> line 1␤␤»

It seems like merely changing $block to &block in the signature would fix the issue, but I'm unsure whether :$label and :$item need to be added to it as well.

Mentioned on IRC as well​: http://irclog.perlgeek.de/perl6-dev/2016-09-22#i_13260484

From @lizmat

AFAIK, :$label en :$item are internal to the setting. They’re needed because internally, map is used for for-loops. And for loops can have a label. And need to be told the list they’re getting should be considered an item.

Regarding why .first and .map exist​: this is because of the way a backtrace is not really a List, but pretends to be. The .list method vivifies 100 elements (if it can), which basically means that the whole backtrace gets vivified to find e.g. the first non-core setting line. Which is expensive.

I think the whole backtrace handling needs to be rethought at some point in time, and probably rewritten from scratch, because at the moment it is a pile of hacks on hacks on hacks. :-(

So I’ve made it a &block, as you suggested.

Closable with tests, I would say :-)

On 23 Sep 2016, at 02​:01, Zoffix Znet (via RT) <perl6-bugs-followup@​perl.org> wrote​:

# New Ticket Created by Zoffix Znet
# Please include the string​: [perl #​129334]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl6/Ticket/Display.html?id=129334 >

This .map multi in Backtrace.pm never gets acccessed​: https://github.com/rakudo/rakudo/blob/553cedb679f0f191d2f7341e05033505cb20ac7a/src/core/Backtrace.pm#L282

<Zoffix> m​: Backtrace.new.map​: {...}
<camelia> rakudo-moar 553ced​: OUTPUT«Ambiguous call to 'map'; these signatures all match​:␤​:(\SELF​: █; :$label, :$item, *%_)␤​:(Backtrace​:D $​: $block, *%_)␤ in block <unit> at <tmp> line 1␤␤»

It seems like merely changing $block to &block in the signature would fix the issue, but I'm unsure whether :$label and :$item need to be added to it as well.

Mentioned on IRC as well​: http://irclog.perlgeek.de/perl6-dev/2016-09-22#i_13260484

The RT System itself - Status changed from 'new' to 'open'

From @zoffixznet

Tests added in Raku/roast@e5bd8d8c54

@zoffixznet - Status changed from 'open' to 'resolved'