http://www.perlmonks.org?node_id=644000


in reply to Any way to access the contents of a block eval?

There's surely some way of recreating the code from optree quite accurately. (See B::Deparse for a module that does something similar.)

However, I don't see the use of this. The contents of an eval BLOCK doesn't change. What's the point of printing out something you already know? What does change is the contents of variables, so there would be value in printing those.

But that's a hard problem. Consider

eval { func_that_uses_globals() };
eval { $big_complex_object->method() };

[download]

How would one programatically determine which variables would be relevant to print? What if the variable doesn't even exist in the eval block because the exception occured in code called by the eval block? I'm sure there are more issues.

Seems to me you'll just have to use the line number in the error message and either manually add code to print out the variables you deem relevant or use a debugger.

By the way, 1/0 (unlike 1/$x) throws an exception eval BLOCK can't catch, because the exception occurs at compile time during constant folding, long before eval is executed.

Replies are listed 'Best First'.
Re^2: Any way to access the contents of a block eval?
by adrianh (Chancellor) on Oct 12, 2007 at 12:56 UTC
    However, I don't see the use of this. The contents of an eval BLOCK doesn't change. What's the point of printing out something you already know?

    I was thinking of nicer default diagnostic messages for Test::Exception - so instead of writing:

    lives_ok { $o->something } 'something worked';

    [download]

    you could just write

    lives_ok { $o->something };

    [download]

    And still get a vaguely nice diagnostic

    ok - $o->something lived

    [download]
[reply]
[d/l]
[select]

      In that case, chromatic's code simplifies to 

      use B::Deparse qw( );

my $deparse = B::Deparse->new();

sub lives_ok(&;$) {
   my ($code, $desc) = @_;
   $desc = $deparse->coderef2text($code)
      if !defined($desc);
   return Text::Exception::lives_ok($code, $desc);
}

      [download]

      Be careful to avoid accidently overriding your own functions with those from the module you are extending.

[reply]
[d/l]
        D'oh! I knew about that.
[reply]

      Ah, so you already have the sub reference. Even easier.

[reply]

In Section Seekers of Perl Wisdom