Teaching Perl

While many people have asked questions about how to teach Perl or where to learn it, an email today on the Perl Advocacy list mentioned a college professor that was not only teaching Perl, but was surprised by the overwhelming demand for it. You read about the course, if you're curious. In just browsing through it, I noticed a few things that were a bit odd, but all in all, it seemed far better than most material out there. Here's one of the questions from a quiz:

 # Given:

 sub pair {
     my @out = ();
     for (my $i=0; $i<@_; $i+=2) {
         push(@out,[$_[$i],$_[$i+1]]);
     }
     return @out;
 }

# What is the value of the expression 

 map { &{$_->[1]}($_->[2]) ? $_->[0] : () }
 map { [$_->[0],$_->[1],'meowmoo'] } 
 &pair ( 'cat' => sub { $_[0] =~ /meow/ }, 
         'dog' => sub { $_[0] =~ /arf/ }, 
         'cow' => sub { $_[0] =~ /moo/ } )

# in an array context?
[download]

Reading through the course information is quite interesting. Enjoy!

Cheers,
Ovid

New address of my CGI Course.
Silence is Evil (feel free to copy and distribute widely - note copyright text)

Comment on Teaching Perl Download Code

Replies are listed 'Best First'.
Re: Teaching Perl by hardburn (Abbot) on Apr 05, 2003 at 23:22 UTC
Break it up peice by peice. `pair` takes a "hash" and creates an AoA. Consider this code: `my @got = pair( . . . );` [download] Where $i is any integer between 0 and `scalar(@got)`, `$got[$i][0]` will contain the "hash" key, and `$got[$i][1]` will contain its value. Taking the map statements in order of execution, the first one is: `my @got2 = map { [$_->[0],$_->[1],'meowmoo'] } @got;` [download] @got2 is also an AoA, but this time containing three elements. The first two are exactly as they are in @got, and the thrid one is always 'meowmoo'. The second map statement is a bit trickier: `my @got3 = map { &{$_->[1]}($_->[2]) ? $_->[0] : () } @got2;` [download] This one needs to be broken up further: `&{$_->[1]} # Get the subroutine referanced in $got2[$i][1] ($_->[2]) ? # Pass in the value of $got2[$i][2] ('meowmoo') $_->[0] : # If the subroutine returned true, then # pass back the key of the "hash" associated # with that subroutine. () # Otherwise, return undef` [download] @got3 is a simple array, and will contain `('cat', undef, 'cow')`. Actually, I'd have to run the code to check if that undef is really there. Hopefully, this is a multiple-choice test and answers with and without the undef are not both present :) If I had to choose, I'd say that it would be. ---- I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident. -- Schemer Note: All code is untested, unless otherwise stated	[reply] [d/l] [select]
Re: Re: Teaching Perl by fokat (Deacon) on Apr 06, 2003 at 05:39 UTC
I think you're 99.5% correct. A `()` is not the same as `undef`. Take a look... `bash$ perl -e 'print join(",", ('meow', (), 'moo')), "\n";' meow,moo` [download] But the rest of the analysis is perfect, so a big ++ for you :) Best regards -lem, but some call me fokat	[reply] [d/l]
Re: Teaching Perl by hsweet (Pilgrim) on Apr 05, 2003 at 22:07 UTC
I just looked over (quickly) the profs site. Dese college guys are smart! Much harder that I do. I'm in the middle of my second time teaching my perl course. High school level to kids with no experience in programming anything more involved than a VCR. I'm happy when they can write a working counter after 10 weeks. (And they can) I've got my course materials up at http://frontiernet.net/~hsweet/programming Time flies like an arrow, fruit flies like banannas	[reply]
Re: Teaching Perl by tbone1 (Monsignor) on Apr 08, 2003 at 12:53 UTC
Interesting ... I've been out of academia for far longer than I'd car to admit, so it is always a bit jarring to be reminded of what a professor thinks is important to know compared to some schlub (like me) who just needs to get something done on a deadline. Still, this looks like another good resource, and I might have to look through it myself to see what I can pick up. If nothing else, it will be good practice for technique and analysis. -- tbone1 Ain't enough 'O's in 'stoopid' to describe that guy. - Dave "the King" Wilson	[reply]


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