There are numerous error messages that highlight perl 5 isms
e.g.
> say $#array;
===SORRY!=== Error while compiling <unknown file>
Unsupported use of $#variable; in Perl 6 please use @variable.end
and
package foo;
===SORRY!=== Error while compiling <unknown file>
This appears to be Perl 5 code. If you intended it to be Perl 6 code, please use a Perl 6 style declaration like "unit package Foo;" or "unit module Foo;", or use the block form instead of the semicolon form.
Yes, these suggestions are among my favorite things about Rakudo.
There are a lot more, too. Another example:
> 1 == 1 ? "sane" : "insane"
===SORRY!=== Error while compiling <unknown file>
Unsupported use of ? and : for the ternary conditional operator; in Perl 6 please use ?? and !!
at <unknown file>:1
Or:
> loop(my $i = 0; $i < 10; $i++) { say $i }
===SORRY!===
Word 'loop' interpreted as 'loop()' function call; please use whitespace around the parens
at <unknown file>:1
Easily the nicest error reporting I've seen in a compiler.
e.g.
and