πŸŽ„ 25/25. Tips and ideas for the Perl 6 Golf code

Welcome to Day 25, the last day of the Perl 6 One-Liner Advent Calendar! Traditional advent calendars have only 24 entries, and our bonus post today will be dedicated to some tips and tricks that you can use in Perl 6 golf contest.

There is a great site, code-golf.io, where you can try solving a number of problems, and move Perl 6 to the top scores. I suspect that many problems can benefit from the techniques that were covered in the previous days of this One-Liner Advent Calendar.

Omitting topic variable

If methods are called on the topic variable $_, then the name of the variable is not really needed for Perl 6 to understand what you are talking about, so, avoid explicitly naming the topic variable:

$_.say for 1..10

Using ranges for making loops

Ranges in Perl are great things to express loop details: in a few characters, you specify both the initial and final state of the loop variable. Postfix forms are usually shorter.

for 1..10 {.say}
.say for 1..10

Think if you can count from 0, in which case, a caret character can be used to get a range starting from 0. The following code prints the numbers 0 to 9:

.say for ^10

Choosing between a range and a sequence

In loops, sequences can work exactly the same as a range would do. The choice may depend on whether the Golf software counts bytes or Unicode characters. In the first case, the two dots of a range are preferable over the three dots of a range. In the second case, use a Unicode character:

.say for 1..10
.say for 1...10
.say for 1…10

When you need to count downwards, sequences are your friends, as they can deduce the direction of changing the loop counter:

.say for 10…1

Using map instead of a loop

In some cases, especially when you have to make more than one action with the loop variable, try using map to iterate over all the values:

(^10).map: *.say

Omitting parentheses

Unlike Perl 5, Perl 6 does not force you to use parentheses in condition checks in the regular form:

if ($x > 0) {say $x;exit}
if $x > 0 {say $x;exit}

Sometimes, you will want to omit parentheses in function calls, too.

Neither you need parentheses when declaring arrays or hashes. With arrays, use the quoting construct on top of that:

my @a = ('alpha', 'beta')
my @b=<alpha beta>

Using chained comparisons

Another interesting feature is using more than one condition in a single expression:

 say $z if $x < 10 < $y

Choosing between methods and functions

In many cases, you can choose between calling a function and using a method. Method calls can be additionally chained after each other, so you can save a lot of parentheses or spaces:

(^10).map({.sin}).grep: *>0 

When there exist both a method and a stand-alone function, method call is often shorter or at least the same length if you omit parentheses.

abs($x)
abs $x
$x.abs

Using Unicode characters

Perl 6 operators often have Unicode equivalents, where you can express a wordy construct with a single character. Compare:

if $x=~=$y
if $x≅$y

Built-in constants are also available in the Unicode space, for example, pi vs Ο€, or Inf vs βˆž.

There are many numbers, both small and big, that can be replaced with a single Unicode symbol: 1/3 vs β…“, or 20 vs β‘³, or 100 vs β…­.

Using superscripts

Superscripts are great for calculating powers. Compare:

say $x**2
$xΒ².say

Using \ to make sigilless variables

Don’t forget about the the following way of binding containers and creating a kind of a sigilless variable:

my \a=42;say a

Using default parameters

When you are working with functions or class methods, check if there are default values in their signatures. Also check if there is an alternative variant with positional arguments. Compare, for example, three ways of creating a date object.

Date.new(year=>2019,month=>1,day=>1)
Date.new(year=>2019)
Date.new(2019,1,1)

Using && instead of if

Boolean expressions can save a few characters, as Perl will not calculate the second condition if the first gives the result already. For example:

.say if $x>0   
$x>0&&.say

Choosing between put vs say

Finally, sometimes it is better to use put instead of say. In some cases, you will be free from parentheses in the output when printing arrays, for example. In some other cases you will get all values instead of concise output when working with ranges, for example:

> say 1..10
1..10
> put 1..10
1 2 3 4 5 6 7 8 9 10

Till next year!

You can also find many interesting ideas in the last year’s advent post by Aleks-Daniel Jakimenko-Aleksejev.

But this time, this Perl 6 One-Line Advent Calendar is completely over. There will be one more post with an overview of everything published in the last 25 days.

I wish you all the best with your further Perl 6 adventure, would it be one-liners or industrial-scale applications. See you next year in another advent calendar, but don’t forget that perl6.online continues its work, and more posts will be published during the next 2019 year!

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