TL;DR

Here we are with TASK #1 from The Weekly Challenge #190. Enjoy!

The challenge

You are given a string with alphabetic characters only: A..Z and a..z.

Write a script to find out if the usage of Capital is appropriate if it satisfies at least one of the following rules:

1) Only first letter is capital and all others are small.
2) Every letter is small.
3) Every letter is capital.

Example 1

Input: $s = 'Perl'
Output: 1

Example 2

Input: $s = 'TPF'
Output: 1

Example 3

Input: $s = 'PyThon'
Output: 0

Example 4

Input: $s = 'raku'
Output: 1

The questions

The specification is a little… lacking, e.g.:

• is the empty string valid?
• does it qualify?
• what should we print exactly? (This is left for induction from the examples).

The solution

Well, this is the perfect challenge for some regular expression.

This is where Perl spoiled me. I feel –no, I know– that there are better ways to express this in Raku, but it worked in the first place and I’ll call it a day.

#!/usr/bin/env raku
use v6;
sub MAIN ($s) { put capital-detection($s) }

sub capital-detection ($string) {
   ($string ~~ /
         ^<[a..z]>*$                # lc
      |  ^<[a..z A..Z]><[a..z]>*$   # ucfirst
      |  ^<[A..Z]>*$/               # uc
   ) ?? 1 !! 0;
}

In Perl I’m setting the start of string and end of string once, then using non-capturing parentheses for the three alternatives.

#!/usr/bin/env perl
use v5.24;
use warnings;
use experimental 'signatures';
no warnings 'experimental::signatures';

say capital_detection(shift // 'whatever');

sub capital_detection ($string) {
   0 + $string =~ m{\A(?:[a-z]*|[a-zA-Z][a-z]*|[A-Z]*)\z}mxs;
}

Stay safe!