From @FROGGS

FROGGS​: m​: multi car($x, [$y, @​ys] where $x == 1) {1}; say car 1, [1,
[2, 3]];
camelia​: rakudo-moar d69491​: OUTPUT«1␤»
FROGGS​: m​: multi car($x, [$y, @​ys] where $x == $y) {1}; say car 1, [1,
[2, 3]];
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»

And also​:
andreoss​: m​: multi car($x, [$y, @​ys] where $x == $y) {1}; say car 1,
[1,2,3];
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»
andreoss​: could that be a bug?
moritz​: m​: say 1 == [1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«False␤»
moritz​: m​: multi car($x, [$y, *@​ys] where $x == $y) {1}; say car 1, [1,
2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»
moritz​: m​: multi car($x, [$y, *@​ys] where { $x == $y }) {1}; say car 1,
[1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»
moritz​: huh
moritz​: m​: multi car($x, [$y, *@​ys] where { say (​:$x, :$y).perl; $x ==
$y }) {1}; say car 1, [1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«("x" => 1, "y" => Mu)␤Cannot call
'infix​:<==>'; none of these signatures match​:␤​:(Any $?)␤​:(Any \a, Any
\b)␤​:(Real \a, Real \b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D
\a, Num​:D \b --> Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D…»
moritz​: m​: multi car($x, @​ [$y, *@​ys] where { say (​:$x, :$y).perl; $x
== $y }) {1}; say car 1, [1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«("x" => 1, "y" => Mu)␤Cannot call
'infix​:<==>'; none of these signatures match​:␤​:(Any $?)␤​:(Any \a, Any
\b)␤​:(Real \a, Real \b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D
\a, Num​:D \b --> Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D…»
moritz​: m​: sub f($x, [$y, *@​ys]) { say (​:$x, :$y, :@​ys).perl }; f 1, [2,
3, 4]
camelia​: rakudo-moar d69491​: OUTPUT«("x" => 1, "y" => 2, "ys" => [3, 4])␤»
moritz​: m​: sub f($x, [$y, *@​ys] where { say $y.perl } ) { say (​:$x, :$y,
:@​ys).perl }; f 1, [2, 3, 4]
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call method 'perl' on a null
object␤ in sub f at /tmp/UT7XBanYbi​:1␤ in block <unit> at
/tmp/UT7XBanYbi​:1␤␤»
moritz​: andreoss​: seems like variables extracted from subsignatures
aren't available in where-blocks
moritz​: andreoss​: and yes, that's a bug

From @AlexDaniel

Interesting. Still reproducible (2017.11, HEAD(5929887))

On 2015-01-14 03​:05​:38, FROGGS.de wrote​:

FROGGS​: m​: multi car($x, [$y, @​ys] where $x == 1) {1}; say car 1, [1,
[2, 3]];
camelia​: rakudo-moar d69491​: OUTPUT«1␤»
FROGGS​: m​: multi car($x, [$y, @​ys] where $x == $y) {1}; say car 1, [1,
[2, 3]];
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»

And also​:
andreoss​: m​: multi car($x, [$y, @​ys] where $x == $y) {1}; say car 1,
[1,2,3];
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»
andreoss​: could that be a bug?
moritz​: m​: say 1 == [1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«False␤»
moritz​: m​: multi car($x, [$y, *@​ys] where $x == $y) {1}; say car 1, [1,
2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»
moritz​: m​: multi car($x, [$y, *@​ys] where { $x == $y }) {1}; say car 1,
[1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call 'infix​:<==>'; none of
these signatures match​:␤​:(Any $?)␤​:(Any \a, Any \b)␤​:(Real \a, Real
\b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D \a, Num​:D \b -->
Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D \a, Rational​:D \b)␤​:(…»
moritz​: huh
moritz​: m​: multi car($x, [$y, *@​ys] where { say (​:$x, :$y).perl; $x ==
$y }) {1}; say car 1, [1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«("x" => 1, "y" => Mu)␤Cannot call
'infix​:<==>'; none of these signatures match​:␤​:(Any $?)␤​:(Any \a, Any
\b)␤​:(Real \a, Real \b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D
\a, Num​:D \b --> Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D…»
moritz​: m​: multi car($x, @​ [$y, *@​ys] where { say (​:$x, :$y).perl; $x
== $y }) {1}; say car 1, [1, 2, 3]
camelia​: rakudo-moar d69491​: OUTPUT«("x" => 1, "y" => Mu)␤Cannot call
'infix​:<==>'; none of these signatures match​:␤​:(Any $?)␤​:(Any \a, Any
\b)␤​:(Real \a, Real \b)␤​:(Int​:D \a, Int​:D \b)␤​:(int $a, int $b)␤​:(Num​:D
\a, Num​:D \b --> Bool)␤​:(num $a, num $b --> Bool)␤​:(Rational​:D…»
moritz​: m​: sub f($x, [$y, *@​ys]) { say (​:$x, :$y, :@​ys).perl }; f 1, [2,
3, 4]
camelia​: rakudo-moar d69491​: OUTPUT«("x" => 1, "y" => 2, "ys" => [3, 4])␤»
moritz​: m​: sub f($x, [$y, *@​ys] where { say $y.perl } ) { say (​:$x, :$y,
:@​ys).perl }; f 1, [2, 3, 4]
camelia​: rakudo-moar d69491​: OUTPUT«Cannot call method 'perl' on a null
object␤ in sub f at /tmp/UT7XBanYbi​:1␤ in block <unit> at
/tmp/UT7XBanYbi​:1␤␤»
moritz​: andreoss​: seems like variables extracted from subsignatures
aren't available in where-blocks
moritz​: andreoss​: and yes, that's a bug

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

Ref Raku/problem-solving#24