This should illustrate what is going on:
use strict;
my $lTokens = [qw(2 * 2)];
print "1 before parse: ", $lTokens, "\n";
my $errmsg = parse($lTokens);
print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
$lTokens = [qw(2 * 2)];
print "2 before parse: ", $lTokens, "\n";
my $errmsg = parse($lTokens);
print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
# -------------------------------------------
sub parse
{
my($lTokens, $callback) = @_;
print "1 parse: ", $lTokens, "\n";
sub gettoken
{
print "1 gettoken: ", $lTokens, "\n";
if (@$lTokens==0)
{
return undef;
}
my $token = shift(@$lTokens);
return $token;
} # gettoken()
my $tok = gettoken();
print("TOKEN: '$tok'\n");
return("Empty Input") if !$tok;
$tok = gettoken();
while ($tok) {
print("TOKEN: $tok\n");
$tok = gettoken();
}
}
On 2/8/06, John Deighan <[EMAIL PROTECTED]> wrote:
> I realize that most things that look like bugs in Perl are in reality
> programmer bugs, but I can't figure out why the second call to the
> function "parse()" in the code below fails. According to my debugger
> (from ActiveState's Perl Development Kit), the function parse() gets
> a correct list of 3 tokens in parameter $lTokens, but when the
> embedded function gettoken() is called, it thinks that $lTokens is an
> empty list. This only happens the second time that parse() is called,
> not the first time. I'm just completely baffled.
>
> P.S. Please don't send me e-mails about how to get this working right
> by modifying the code. I'm sure I can do that, and besides, the real
> code is considerably more complicated than this. I want to know why
> this code does not work as I expect. Anyway, here's the code and the
> output I get (I'm running ActivePerl 5.8.7 Build 815 under Windows
> 2000 Server):
>
> use strict;
>
> my $lTokens = [qw(2 * 2)];
> my $errmsg = parse($lTokens);
> print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
>
> $lTokens = [qw(2 * 2)];
> my $errmsg = parse($lTokens);
> print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
>
> # -------------------------------------------
>
> sub parse { my($lTokens, $callback) = @_;
>
> sub gettoken {
>
> if (@$lTokens==0) {
> return undef;
> }
> my $token = shift(@$lTokens);
> return $token;
> } # gettoken()
>
> my $tok = gettoken();
> print("TOKEN: '$tok'\n");
> return("Empty Input") if !$tok;
> $tok = gettoken();
> while ($tok) {
> print("TOKEN: $tok\n");
> $tok = gettoken();
> }
> }
>
>
> ---------------
> OUTPUT:
> ---------------
> C:\Scripts>testGrammar2.pl
> TOKEN: '2'
> TOKEN: *
> TOKEN: 2
> OK
> TOKEN: ''
> ERROR: Empty Input
>
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