WhateverCode on the LHS of ~~ (trap?)

[AlexDaniel]

A question on #perl6 channel was asked today:

my @a = <1 2 3>; say @a.grep( *.Int ~~ 2 );

Cannot use Bool as Matcher with '.grep'.  Did you mean to use $_ inside a block?
  in block <unit> at <tmp> line 1

why is this? why doesn't this dwim?

Followed by:

<geekosaur> I thought this was a listed/known trap

Yet I don't see it listed on the traps page. We have a similar item there… similar but completely different. That being said, the trick that is mentioned there still applies:

my @a = <1 2 3>; say @a.grep( 2 ~~ *.Int );

(2)

However, more common solution to this is to use a block instead:

my @a = <1 2 3>; say @a.grep( {.Int ~~ 2} );

(2)

[tisonkun]

IMO it's a trap, for
*.Int ~~ 2 equals 2.ACCEPTS(*.Int), and return False
2 ~~ *.Int equals *.Int.ACCEPTS(2) and it is a instance of WhateverCode