Perl and Raku solutions to Task 1 of the Perl Weekly Challenge #060

On branch branch-for-challenge-060
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	new file:   challenge-060/athanasius/perl/ch-1.pl
	new file:   challenge-060/athanasius/raku/ch-1.raku

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+#!perl
+
+################################################################################
+=comment
+
+Perl Weekly Challenge 060
+=========================
+
+Task #1
+-------
+*Excel Column*
+
+*Reviewed by: Ryan Thompson*
+
+Write a script that accepts a number and returns the *Excel Column Name* it
+represents and vice-versa.
+
+Excel columns start at *A* and increase lexicographically using the 26 letters
+of the English alphabet, *A*..*Z*. After *Z*, the columns pick up an extra
+"digit", going from *AA*, *AB*, etc., which could (in theory) continue to an
+arbitrary number of digits. In practice, Excel sheets are limited to 16,384
+columns.
+
+*Example*
+
+Input Number: 28 Output: AB
+
+Input Column Name: AD Output: 30
+
+=cut
+################################################################################
+
+#--------------------------------------#
+# Copyright © 2020 PerlMonk Athanasius #
+#--------------------------------------#
+
+use strict;
+use warnings;
+use Const::Fast;
+use Scalar::Util qw( looks_like_number );
+use constant WARN_ON_RANGE => 1;
+
+const my $MAX_COLUMN => 16_384;                  # = XFD: 24*26² + 6*26¹ + 4*26⁰
+
+#-------------------------------------------------------------------------------
+BEGIN
+#-------------------------------------------------------------------------------
+{
+    $| = 1;
+    print "\n";
+}
+
+#===============================================================================
+MAIN:
+#===============================================================================
+{
+    print "Challenge 060, Task #1: Excel Column (Perl)\n\n";
+
+    my $args = scalar @ARGV;
+       $args == 1
+            or die "ERROR: Expected 1 command-line argument but found $args\n";
+
+    my $arg = $ARGV[0];
+
+    if (looks_like_number($arg))
+    {
+        int($arg) == $arg && $arg > 0
+            or die "ERROR: Invalid numeric argument \"$arg\"\n";
+
+        warn "WARNING: Column $arg is out of range\n"
+            if WARN_ON_RANGE && $arg > $MAX_COLUMN;
+
+        my $name = number_to_name($arg);
+
+        print "The Excel column number $arg is named \"$name\"\n";
+    }
+    else
+    {
+        my $name = uc $arg;
+           $name =~ / ^ [A-Z]+ $ /x
+                or die "ERROR: Argument \"$arg\" is not a valid column name\n";
+
+        my $number = name_to_number($name);
+
+        warn "WARNING: Column \"$name\" is out of range\n"
+            if WARN_ON_RANGE && $number > $MAX_COLUMN;
+    
+        print "The Excel column named \"$name\" is number $number\n";
+    }
+}
+
+#-------------------------------------------------------------------------------
+sub number_to_name
+#-------------------------------------------------------------------------------
+{
+    my ($num) = @_;
+    my  $name = '';
+    my  $exp  =  2;
+    my  $max  = 26;                                 # Cf. OEIS A218729:
+        $max += 26 ** $exp++ while $max < $num;     #     1, 27, 703, 18279, ...
+
+    for my $power (reverse 0 .. $exp - 2)
+    {
+        my $div   = 26 ** $power;
+        my $quo   = int($num / $div);
+           $quo   = 26 if $quo > 26;
+           $name .= ('A' .. 'Z')[$quo - 1];
+           $num  -= $quo * $div;
+
+        last if $num == 0;
+    }
+
+    return $name;
+}
+
+#-------------------------------------------------------------------------------
+sub name_to_number
+#-------------------------------------------------------------------------------
+{
+    my ($name)  = @_;
+    my  $number = 0;
+
+    for (my $multiplier = 1; $name; $multiplier *= 26)
+    {
+        my $char = substr $name, -1, 1, '';
+        $number += $multiplier * (ord($char) - ord('A') + 1);
+    }
+
+    return $number;
+}
+
+################################################################################