Why is this program valid? I was trying to create a syntax error

Question

I'm running ActiveState's 32 bit ActivePerl 5.14.2 on Windows 7. I wanted to mess around with a Git pre-commit hook to detect programs being checked in with syntax errors. (Somehow I just managed to do such a bad commit.) So as a test program I randomly jotted this:

use strict;
use warnings;

Syntax error!

exit 0;

However, it compiles and executes with no warnings, and errorlevel is zero on exit. How is this valid syntax?

Answer 1

Perl has a syntax called "indirect method notation". It allows

Foo->new($bar)

to be written as

new Foo $bar

So that means

Syntax error ! exit 0;

is the same as

error->Syntax(! exit 0);

or

error->Syntax(!exit(0));

Not only is it valid syntax, it doesn't result in a run-time error because the first thing executed is exit(0).

Answer 2

I don't know why, but this is what Perl makes of it:

perl -MO=Deparse -w yuck
BEGIN { $^W = 1; }
use warnings;
use strict 'refs';
'error'->Syntax(!exit(0));
yuck syntax OK

It seems that the parser thinks you're calling the method Syntax on the error-object... Strange indeed!