Unwrapping the second gift brought to you by Perl 6 this Advent, we find… a method named .fmt
.
If you’re familiar with sprintf
, you’ll feel right at home with .fmt
. If you haven’t heard about sprintf
before, or if you’ve heard of it but are a bit fuzzy on the details, you might want to skim the perldoc page. Don’t drown in it, though; it’s longish. Just savour it.
Back to .fmt
, sprintf
‘s spunky little sister. Here are a few ways to use .fmt
to format strings and integers.
say 42.fmt('%+d') # '+42' say 42.fmt('%4d') # ' 42' say 42.fmt('%04d') # '0042' say :16<1337f00d>.fmt('%X') # '1337F00D'
All this is good and well, but not really more than a shorter method form of sprintf
. Big deal, right?
What I haven’t told you yet is that .fmt
is overloaded, and works differently on arrays (or more precisely, lists):
say <huey dewey louie>.fmt # 'huey dewey louie' say <10 11 12>.fmt('%x') # 'a b c' say <1 2 3>.fmt('%02d', '; ') # '01; 02; 03'
Similarly, it’s overridden on hashes (or rather, mappings):
say { foo => 1, bar => 2 }.fmt # 'foo 1 # bar 2'
say { Apples => 5, Oranges => 10 }.fmt('%s cost %d euros') # 'Apples cost 5 euros # Oranges cost 10 euros'
say { huey => 1, dewey => 2, louie => 3 }.fmt('%s', ' -- ') # 'huey -- dewey -- louie'
The way hashing works may give your output a different order than the ones shown above. Oh, and there’s an overloaded .fmt
for pairs as well, but it works analogously to the one for hashes.
.fmt
is a useful little tool to have when you want to change some value, or an array or a hash of values, into to some given format. It’s like sprintf
, but tailored to Do What You Mean for arrays and hashes, too.
There’s only one risk in all of this: Perl 6 might soil the reputation of the Perl family of languages by simply being too darn readable. In order to counter this risk, I leave a small parting gift in the form of a simple-but-dense Christmas tree printing Perl 6 one liner:
$ perl6 -e 'say " "x 9-$_, "#"x$_*2-1 for flat 0..9,2 xx 3' # ### ##### ####### ######### ########### ############# ############### ################# ### ### ###
c:\>perl6.exe -e "say ' 'x 9-$_,'#'x$_*2-1 for flat 0..9,2 xx 3"
Excellent article!!
Is there any way to have fmt produce “huey, dewey, and loiue” from ?
Seems like that one is needed alot too.
Great article indeed. What a good resource initiative for Perl 6. Keep it up!
Aloha, Will! There’s no built-in way to do what you want, but one can easly write a custom .fmt method that has a different last separator: I wrote one here just to make sure it works.
Carl, Thanks for the code!! I’m just now starting to see the light at the end of the Perl6 tunnel.
Cool! But use .kv to get index from array in for statement, it will look much more perl6ish :)
I started out writing it that way, but ran into unexpected trouble with Rakudo. And after I changed it, people told me this version was clearer. Though in retrospect, I think I agree that .kv would have been both more idiomatic and nicer. :)
After the Great List Refactor, the following code works for creating the Christmas tree:
perl6 -e ‘say ” “x 9-$_, “#”x$_*2-1 for (0..9,2 xx 3).flat’
Oops, Without smart quotes:
perl6 -e ‘say " "x 9-$_, "#"x$_*2-1 for (0..9,2 xx 3).flat’
Trying to paste without smart quotes once more:
Thank you; updated!