Greetings, Monks.

In my weary travels, I have found a serene beauty in your language. It is sometimes harsh, but it is also beautiful. I come from the land of Python, were folks carry their language as a hammer, always clear and to the point. However, at times I wish that I can wield a rapier, swift and effective. Which is why I come to the Monastery.

Recently, I have started looking at problems on Rosalind (rosalind.org) and decided to solve all the tasks in Perl. Question number 1 is particularly interesting. It is simple, yet writing clean code for it may be a challenge. The task is simple - count letters in a string and print counts in alphabetical order.

Here is what I came up with

#!/usr/bin/env perl
#Question 1: Counting DNA nucleotides
use v5.16;

sub sort_and_print_hash_keys (\%) {
    my %hash = %{shift()};
    foreach (sort keys %hash) {
        print "$hash{$_} ";
    }
    print "\n";
}

sub counting {
    my %letters = ();

    chomp(my $seq = readline);

    foreach my $base (split //, $seq) {
        $letters{$base}++;
    }

    sort_and_print_hash_keys(%letters);
}

counting();

[download]

As you might see, I like clean and meaningful code. One thought per line.

My question is twofold. First, is this idiomatic Perl? Would you have done something differently? Please, critique this.

Second, I am wondering if the magic behind hash ref passing has any side effects. Here, I use a subroutine prototype declaration to ensure argument type safety and dereference immediately with %{shift()}. Are there any undesired consequences of this? Does any other code flatten out data structures or makes unnecessary copies? I am aware that 'sort keys' would create a separate array of keys.

Thank you, monks. I eagerly await your wisdom

In reply to Entering the land of Perl by manbroski

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