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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