A few years ago, I wrote a module called Loop.pm
which I believe does what you want.
http://cpan.uwinnipeg.ca/~gslondon/Loop
Here's how you Loop through an array:
use Loop;
my @array = qw (alpha bravo charlie);
Loop::Array @array, sub
{
my ($index,$value)[EMAIL PROTECTED];
print "at index '$index', value='$value'\n";
}
This example will return a list of keys that are contained in their
corresponding value.
my %hash = qw
(
aaa bebaaa
abc xyz
root taproot
oingo boingo
billy bob
);
@key_is_in_value = Loop::Hash %hash, sub
{
my($key,$val)[EMAIL PROTECTED];
if($val=~/$key/)
{return $key;}
else
{return;}
};
Hashes can have nested loops, which avoids the perl builtin "each" problem of
having a place holder for only one iterator.
Files can be looped through providing a quick and easy way to open, read, and
close a file, including error handling on failures to open, and providing the
current line number for your code.
It does all the work for you in one call.
# print first 10 lines of file, along with each line's line number.
Loop::File "tfile.pl", sub
{
my($linenum,$linestr)[EMAIL PROTECTED];
print "$linenum \t: $linestr";
$_[-1]='last' if ($linenum == 10);
};
All is not perfect in Loop.pm, though.
Constructs such as "next" and "last"
are not available, since it isn't really
a lexical loop that the parser can find.
Instead, what you do is assign a string
to $_[-1], and the string will be 'next'
or 'last'. The looping wrapper will then
do the right thing.
Greg
________________________________
From: [EMAIL PROTECTED] on behalf of Palit, Nilanjan
Sent: Thu 9/21/2006 12:34 PM
To: [email protected]
Subject: Re: [Boston.pm] Loop index in foreach?
Uri,
Using both the array element value & index in a loop is a very
fundamental coding usage (just like using the hash key & value), which I
didn't think needed further elaboration (it's not exactly an esoteric
usage model!). Nevertheless, here is an example I'm currently working
on (which prompted the question):
I'm parsing a Verilog assign statement & the RHS is a multi-bit
concatenated bus. The key on the LHS includes the "[$i]", so I can use
that to correlate the same signal to another place in the code:
my $i= 0;
foreach (@sigs)
{ $mybus{"bus1[$i]"}= $_; $i++; }
I think it'd be fairly easy for Perl to auto initialize & increment a
loop index in all loops & provide that to the user in a special
variable. "$." is an excellent example. I think it'd be a great addition
to Perl's excellent (& long) list of special vars, making for yet more
elegant & concise code.
The "push(@newarray[$_], ..." in my original example was a bad typo -- I
did not intend the '[$_]' ... Thanks for flagging that.
Thanks,
-Nilanjan
-----Original Message-----
From: Uri Guttman [mailto:[EMAIL PROTECTED]
Sent: Monday, September 18, 2006 12:09 PM
To: Palit, Nilanjan
Cc: [email protected]
Subject: Re: [Boston.pm] Loop index in foreach?
>>>>> "PN" == Palit, Nilanjan <[EMAIL PROTECTED]> writes:
PN> That works too (& I have used it as well), but I guess what I'm
PN> really asking (hoping?) for is a Perl special variable, kinda like
PN> "$.", which Perl auto-magically initializes & increments ...
in my experience classic loop indexes are rarely needed in perl. my take
is that coders who want an index value haven't done a proper design. if
you explain the larger problem i bet we could show you ways to bypass
your perceived need for a loop index.
also in your example you are pushing to @newarray[$i] which is not good
perl as it is an array slice with a single index. this will trigger a
warning if you enable warnings. if all you wanted to do was push some
values onto an new array, then map is your answer as someone else
showed. but anyhow we would like to see more info about the problem so
we can help solve it at the proper level.
uri
--
Uri Guttman ------ [EMAIL PROTECTED] --------
http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and
Coding-
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