📘 Increasing digits by one using Perl 6

📘 Increasing digits by one using Raku

N. B. Perl 6 has been renamed to Raku. Click to read more.


In the given integer number, replace all the digits so that 1 becomes 2, 2 becomes 3, etc., and 9 becomes 0.

This task can be approached both mathematically and string-wise. In Perl 6, regexes seem to be the best match. Although a number is an example of the numeric data type, Perl 6 allows seamless changes when you want to start working with them as with strings.

In the proposed solution, a number is matched against a regex.

my $number = 564378901;
$number ~~ s:g/ (\d) /{ ($0 + 1) % 10 }/;
say $number;

Similar to the code of Task 76, Double each character, a global replacement happens. The target is a digit, \d. (We ignore the fact that the \d character class matches 580 different characters in the Unicode space, see Task 39, Unicode digits.)

So, a digit (treated as a character) lands in the $0 variable. In the replacement part of s///, a block of code is placed. It takes the value of $0 and adds 1 to it. As the + operator expects numeric operands, the character is converted to an integer and is incremented after it. The modulo operator keeps the value in the range between 0 and 9 (including), The new value is converted back to a string character, which replaces the original digit that was captured.

In the given example, 675489012 is printed.Notice that it was not possible to use an increment operator in the replacement. An attempt to make it $0++ would lead to an exception as the ++ operator needs a mutable object.

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