Re: Re: Never lock $0 inside of a BEGIN block

[demerphq]

Why does

 1    #!perl
 2    # Utility vars
 3    
 4    my $foo="Hello there"
 5    
 6    # End utility vars. When do we make these go away?
 7    
 8    ######################################################
 9    # We loop over each character and print them out
10    # this is mostly so that we can do the fnorzle with
11    # boopat over the dulwhup. Which can really pjorn your
12    # noodle
13    
14    
15    for my $i (0.. length($foo)-1) {
16        print "$i ",substr($foo,$i,1),"\n";
17    }

produce the following error

syntax error at D:\perl\scratch\errors.pl line 15, near "$i ("
Execution of D:\perl\scratch\errors.pl aborted due to compilation erro
+rs.

I dont see why this doesn't produce something more intelligent. My general rule for perl errors is that if I don't see the problem immediately on the line that perl tells me I look on the one before, and as the contrived example shows here that can be quite a ways before.

:-)

---
demerphq

_{<Elian> And I do take a kind of perverse pleasure in having an OO assembly language...}

[halley]

Because the following syntax is valid (even if nonsensical):

my $foo = "Hello there" for (1 .. 3);

An upshot of the modifier forms of 'for' and 'if' is that you can make C-style static variables with

sub blah
{
  my $foo if 0;
  print $foo++,$/;
}
blah(),blah(),blah();

Though Larry says it's an accident of implementation that this works...

--
[ e d @ h a l l e y . c c ]

[demerphq]

Heh. Ive encountered a bunch of weirdness with using my and modifiers. (I've even argued that it should produce a warning.) I haven't seen the static variable trick. Thats scary. Cool Scary though. :-)

However I'm still not convinced that this error message couldn't be improved.

BTW, the static trick only works with if 0; and for (); and thus I still consider it something that should produce a warning.

Read more... (821 Bytes)

# No assignment        #With assignment 
for_blah        0      for_blah        0
for_blah        0      for_blah        0
for_blah        0      for_blah        0
---                    ---              
not_for_blah    0      not_for_blah    0
not_for_blah    1      not_for_blah    1
not_for_blah    2      not_for_blah    2
---                    ---              
if_blah         0      if_blah         1
if_blah         0      if_blah         1
if_blah         0      if_blah         1
---                    ---              
not_if_blah     0      not_if_blah     0
not_if_blah     1      not_if_blah     1
not_if_blah     2      not_if_blah     2
---                    ---


---
demerphq

_{<Elian> And I do take a kind of perverse pleasure in having an OO assembly language...}

[ChemBoy]

BTW, the static trick only works with if 0; and for ();

Not so. Observe:

#!/usr/local/bin/perl -l

sub horror { 
    my $foo if "reset" eq shift; 
    print ++$foo;
}

horror($_) for qw(foo bar baz reset bing bang boom);
__END__
1
2
3
4
1
2
3

(Not that the sub name is intended as an editorial comment, or anything... <grin>)

The nasty part is just that the cleanup (resetting $foo to undef) takes place at the end of the iteration in which my $foo is actually executed (which isn't exactly what you'd expect from a "reset" argument, but that's what you get with silly example code).




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If God had meant us to fly, he would *never* have given us the railroads.
    --Michael Flanders