Advent Calendar - December 10, 2019

Tuesday, Dec 10, 2019| Tags: Raku

Advent Calendar 2019


The gift is presented by Mark Senn. Today he is talking about his solutions to Task #1: Split word on change of character of “The Weekly Challenge - 020”.


Write a script to accept a string from command line and split it on change of character. For example, if the string is “ABBCDEEF”, then it should split like “A”, “BB”, “C”, “D”, “EE”, “F”.


“There’s more than one way to do it” is a Perl programming motto. I decided to solve this using a Raku regex. In my opinion, if you do much programming with character strings, regexes are too powerful to not learn.

See for how to define a MAIN sub. For this program, only a single string from the command line needs to be accepted with no options and the following will suffice. This is nice because if I used a sub MAIN here, I would put all of the code below indented inside the sub MAIN.

The Raku regex:

 /((.){}$0 *)*/;

with no comments could be used. For this regex I prefer commenting it like below to explain it to people who may have not used regexes before.

Search for the quoted comments in the code below in here for more information.


use v6.d;

$_ = shift @*ARGS;

/                 # Start a Raku regex (called "regular expression" in Perl).
    (                 # Start a group to match a string of identical characters.
        (.)               # Match a single character.
        {}                # "This code block publishes the capture inside the
                          # regex, so that it can be assigned to other variables
                          # or used for subsequent matches."
        $0*               # Match the previously matched character
                          # zero or more times.
    )*                # End the group to match a string of identical characters.
                      # There are zero or more groups of identical characters.
/;                # End the Raku regex.

# "Coercing the match object to a list gives an easy way
# to programmatically access all elements :"

say $/.list.join;


If you have any suggestion then please do share with us perlweeklychallenge@yahoo.com.

Advent Calendar 2019

SO WHAT DO YOU THINK ?

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