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Comment by jayvanguard | Hacker News Reader

It was explicitly not a design goal to be backwards compatible.

"In exchange for breaking backwards compatibility, at least at the language level, Perl 6 offers plenty of high-powered language concepts that Perl 5 didn't support..."

http://www.perl.com/pub/2006/01/12/what_is_perl_6.html

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That's not what I read the GP post as saying though. Rather, that the perl 6 interpreter could run code written as perl 5 (and never ported). With their different semantics, the results would be unpredictable and often undesired.

From this document, the chance that a perl 5 script is syntactically valid (but semantically different) perl 6 is awfully low. Now if the errors that arose said that you might be trying to execute perl 5 as perl 6, that'd be cool ;)

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.

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