From @labster

07​:02 labster m​: multi sub prefix​:<|> (\a) { a.flat }; say
(|[1,2,3]).perl
07​:02 camelia rakudo-moar d6430c​: OUTPUT«5===SORRY!5=== Error while
compiling /tmp/jvrQI4RBsS␤Arg-flattening | is only valid in an argument
list␤at /tmp/jvrQI4RBsS​:1␤------> 3i sub prefix​:<|> (\a) { a.flat }; say
(|7⏏5[1,2,3]).perl␤»

Expected, one of​:
A) single pipe works as shorthand for flat outside of arg list
B) Rakudo allows me to define my own flat operator (though, in this case,
prefix​:<|||> does work)

Maybe this should be notabug, but if so I'd like an explanation as to why
neither A nor B should work.

From @pmichaud

On Tue, Jun 16, 2015 at 09​:28​:28PM -0700, Brent Laabs wrote​:

07​:02 labster m​: multi sub prefix​:<|> (\a) { a.flat }; say
(|[1,2,3]).perl
07​:02 camelia rakudo-moar d6430c​: OUTPUT«5===SORRY!5=== Error while
compiling /tmp/jvrQI4RBsS␤Arg-flattening | is only valid in an argument
list␤at /tmp/jvrQI4RBsS​:1␤------> 3i sub prefix​:<|> (\a) { a.flat }; say
(|7⏏5[1,2,3]).perl␤»

Expected, one of​:
A) single pipe works as shorthand for flat outside of arg list
B) Rakudo allows me to define my own flat operator (though, in this case,
prefix​:<|||> does work)

Maybe this should be notabug, but if so I'd like an explanation as to why
neither A nor B should work.

Unary | already has a defined syntactic meaning in Perl 6 (argument
list interpolation -- see S06 / Flattening argument lists).

In Rakudo unary | is a syntactic construct that can't be overloaded.

So, notabug. :)

Pm

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

From @pmichaud

On Wed, Jun 17, 2015 at 12​:24​:04AM -0500, Patrick R. Michaud wrote​:

In Rakudo unary | is a syntactic construct that can't be overloaded.

So, notabug. :)

More directly to the comment about unary | possibly working outside of
argument lists, I'm not sure we want to enable the case where unary-|
means something very different outside of an argument list than in it.
I suspect it could be made to do so, however, in which case (| ... )
would be a valid flattening syntax. But I see significant confusion
potential here, which is perhaps best avoided.

Pm

From @jnthn

On Tue Jun 16 22​:24​:27 2015, pmichaud wrote​:

On Tue, Jun 16, 2015 at 09​:28​:28PM -0700, Brent Laabs wrote​:

07​:02 labster m​: multi sub prefix​:<|> (\a) { a.flat }; say
(|[1,2,3]).perl
07​:02 camelia rakudo-moar d6430c​: OUTPUT«5===SORRY!5=== Error
while
compiling /tmp/jvrQI4RBsS␤Arg-flattening | is only valid in an
argument
list␤at /tmp/jvrQI4RBsS​:1␤------> 3i sub prefix​:<|> (\a) { a.flat };
say
(|7⏏5[1,2,3]).perl␤»

Expected, one of​:
A) single pipe works as shorthand for flat outside of arg list
B) Rakudo allows me to define my own flat operator (though, in this
case,
prefix​:<|||> does work)

Maybe this should be notabug, but if so I'd like an explanation as to
why
neither A nor B should work.

Unary | already has a defined syntactic meaning in Perl 6 (argument
list interpolation -- see S06 / Flattening argument lists).

In Rakudo unary | is a syntactic construct that can't be overloaded.

So, notabug. :)

Agree "notabug" in that sense. However, we can always go above and beyond that and note that such a thing will never work out. Now it does this​:

$ perl6-m -e "multi sub prefix​:<|> (\a) { a.flat }"
===SORRY!=== Error while compiling -e
Cannot override prefix operator '|', as it is a special form handled directly by the compiler
at -e​:1
------> sub prefix​:<|><HERE>($x) { }

Tested in S32-exceptions/misc.t.

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