[Ilugc] [TIP] perl tutorial VII (perl tricks)
- From: suraj@xxxxxxxxxxxxx (Suraj Kumar)
- Date: Sat, 10 Dec 2011 09:17:50 +0530
On Fri, Dec 9, 2011 at 8:24 AM, Girish Venkatachalam <
girishvenkatachalam at gmail.com> wrote:
I have not yet understood how map() works. It is a functional
programming concept.
map is a means of transforming ("mapping") an array into another array. The
arguments to map are:
1. function which will take one element at a time and return one element
2. the array of elements
As an example, if one would like to calculate the square of numbers in an
array and store them in another array, one can use map to do it as follows:
@x = (1,2,3,4,5);
@y = map { $_ * $_; } @x;
or simply
@y = map { $_ * $_; } (1, 2, 3, 4, 5);
When map invokes the provided function (first arg) it is called with $_ set
to each element of the array and is called one time for each element in the
order of appearance of its arguments. Let's use map now to also print the
array @y:
map { print $_ . "\n"; } @y
1
4
9
16
25
Here is an exercise to the reader: Using a combination of regexes and map,
read a HTML file and turn all its <a href="(.*?)">(.*?)</a> into a hash
where the URI is the key of the hash and the marked up text (anchor text)
becomes the value. The following is a sample test input string:
$string = <<EOM;
<a href="/blah">Go to blah</a> and <a href="/blah/search">look for all the
blahs</a>... and here is a <a href="/multi">multi
line
<em>nested</em> HTML markup
</a>
EOM
In a lot of ways perl is messy and with a syntax that is so odd that
it is often called
"The write once forget language"
In other words perl is used for quick and dirty jobs.
I'd once again request you to stop demeaning the stuff you're trying to
teach (or thrust your impartial views onto a public forum like this). Why
would anyone want to learn something that is, according to your narrow
understanding, is worthless?
If you think something is tough, it will remain tough and unapproachable
(because the problem of 'toughness', etc., is in your mind). If you're full
of your own preconceived notions, it is very difficult to change it unless
you're willing to throw away those notions and then explore and learn about
it (there is nothing to lose when learning, except time :) ).
Think about it, programming a computer was not any friendlier back then,
yet, that is what paved way for generic abstractions that allowed us to
build cooler stuff on top. Perl too, if you approached it this way, can be
effectively used to abstract away problems and build generic solutions on
top. But you should be willing to invest time in abstracting and designing
your code thus. If you expect a scissor to do what a chainsaw can (and vice
versa) then it is not the tool that is at fault.
Perl on the other hand is a high level language. It is a scripting
language; which means that it is a
language used to express your ideas in a language that looks like English.
This could be said of python but perl is not even half as elegant.
An illiterate will (almost always) write horrible poetry. This is a highly
subjective (and highly inflammable ;) ) bait. Perhaps you're judging perl
by your (or your peers') inability to write elegant code? A sword, to a
Samurai, is more elegant than a pistol.
Why was I not forced to learn Python deeply? But perl is something I
use everywhere. This should give you a hint.
For that matter, why were you not forced to learn even perl deeply?
Cheers,
-Suraj
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Career Gear - Industry Driven Talent Factory
http://careergear.in/
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