Your instinct is correct. Simplest, most important suggestion: always "use warnings;" when developing and testing code.
Ok... I know you asked not to receive rewritten code -- but your parse / gettoken functions cries out for simplification. The sole purpose of your two functions is to get the elements from the array referenced by $lTokens and then process each token / array element. The simple solution is "while (my $tok = shift(@$lTokens)) { #do something with $tok }".
The following is your sample code -- with your parse function renamed to "oldparse", a new parse function "newparse", warnings enabled, and function prototypes specified. [And yes I realize that "Perl Best Practices" says not to use function prototypes -- but I like to use them to catch parameter mismatches such as exist in your example code. Your "parse" expected two parameters but you only passed one -- but is not the source of your problem.] This will produce a warning message that explains the problem with $lToken in the embedded function gettoken.
Regards,
... Dewey
---CODE---
use strict;
use warnings;
sub newparse ($;$);
sub oldparse ($;$);
my $lTokens = [qw(2 * 2)];
my $errmsg = newparse($lTokens);
print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
$lTokens = [qw(3 * 3)];
$errmsg = newparse($lTokens);
print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
$lTokens = [qw(4 * 4)];
$errmsg = oldparse($lTokens);
print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
$lTokens = [qw(5 * 5)];
$errmsg = oldparse($lTokens);
print($errmsg ? "ERROR: $errmsg\n" : "OK\n");
exit(0);
# -------------------------------------------
sub newparse ($;$) {
my($lTokens, $callback) = @_;
while (my $tok = shift(@$lTokens)) {
print("TOKEN: $tok\n");
#call the callback with $tok?
}
return;
}
sub oldparse ($;$) {
my($lTokens, $callback) = @_;
sub gettoken {
if (@$lTokens==0) { #line 40
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");
$tok = gettoken();
}
}
----- Output -----
Variable "$lTokens" will not stay shared at testtoken.pl line 40.
TOKEN: 2
TOKEN: *
TOKEN: 2
OK
TOKEN: 3
TOKEN: *
TOKEN: 3
OK
TOKEN: '4'
TOKEN: *
TOKEN: 4
OK
Use of uninitialized value in concatenation (.) or string at testtoken.pl line 5
0.
TOKEN: ''
ERROR: Empty Input
| John Deighan <[EMAIL PROTECTED]>
Sent by: [EMAIL PROTECTED] 02/08/2006 09:40 AM |
|
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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