Re: Teaching Perl

[hardburn]

in reply to Teaching Perl

Break it up peice by peice.

pair takes a "hash" and creates an AoA. Consider this code:

my @got = pair( . . . );

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;

@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;

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

@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

[fokat]

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

But the rest of the analysis is perfect, so a big ++ for you :)

Best regards

-lem, but some call me fokat