in reply to Re^4: A short whishlist of Perl5 improvements leaping to Perl7 (Thought Experiment No.1)
in thread A short whishlist of Perl5 improvements leaping to Perl7

While the former thought experiment was closer to Python's behavior - all vars belong (mostly) to function scope - there is another possible approach.

1. any assignment to a new variable leads to an implicit my but only if their was no previous explicit declaration in a surrounding scope. This will replace former rules 1,4 and 5 all others still apply

Hence we get the following 4 cases for explicit declarations with my or our

automine effect comment 
{ 
    $x = 1;
    {
        $x = 2;
    }
}

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{ 
    my $x = 1;
    {
        my $x = 2;
    }
}

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 not strict w/o automine 
{ 
    $x = 1;
    {
        my $x = 2;
    }
}

[download]
 
{ 
    my $x = 1;
    {
        my $x = 2;
    }
}

[download]
 not strict w/o automine 
{ 
    my $x = 1;
    {
        $x = 2;
    }
}

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{ 
    my $x = 1;
    {
        $x = 2;
    }
}

[download]
 backwards compatible 
{ 
    my $x = 1;
    {
        my $x = 2;
    }
}

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{ 
    my $x = 1;
    {
        my $x = 2;
    }
}

[download]
 backwards compatible

Surprises and pitfalls:

automine effect comment 
sub foo { 
    if (1) {
        $x = 2;
    }
    print $x;
}

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sub foo { 
    if (1) {
        my $x = 2;
    }
    print $x;     # undeclared
}

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 Doesn't compile

Surprising for Pythonistas 

sub add { 
    $x = 0;
    for (1..9) {
        $x = $x + $_;
    }
    print $x;
}

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sub add { 
    my $x = 0;
    for (1..9) {
        my $x = $x + $_;
    }
    print $x;         # prints 0
}

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 Unexpected result!

Needs an explicit my $x = 0 at init to avoid implicit my

This is a very Perlish approach and avoids many edge cases.

Of course this laziness comes with a price, introducing a new explicit declaration on file scope has an effect at the distance and could silently break subroutines

use automine
# our $var;

... 

sub foo {
    $var = shift; # not 'my $var' if explicit 'our $var' exists 
    ...
}

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That's why this theoretical pragma must be optional. (Of course scoping the our inside a tight block would also prevent this.)

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

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