Perl Weekly Challenge 98: reading chars and inserting in array

One way to let me improve my knowledge about Raku (aka Perl 6) is to implement programs in it. Unluckily, I don’t have any production code to implement in Raku yet (sob!). So, why not try solving the Perl Weekly Challenge tasks?

In the following, the assigned tasks for Challenge 98.

My eyes…

I’m waiting and hoping for another consultancy, the next week, by another specialied center.

PWC 98 - Task 1

The first task was quite simple: reading a specific amount of chars from a file, given its filename. However, there was a little trick: every time a new read was asked for, the file pinter need to increase and resume therefore the reading state.
The problem asked for the definition of a readN function, and I decided to use an hash to store file handles associated to the filename itself. With this in mind, it was easy to resume a reading whenever a new read for the same file is asked. Instead of using a global variable, I decide to use a state variable, that is initialized only the first time the function is called, and therefore can be used later on.
The resulting function is therefore as simple as:

sub readN( Str $file-name, 
           Int $how-many-chars where { $how-many-chars >= 1 } ) {
    state %handles = ();
    %handles{ $file-name } //= $;
    return %handles{ $file-name }.readchars: $how-many-chars;

If a file stream is found in the %handles hash, the stream is used and readchars is called. Otherwise, the hash is initialized by means of //= with a new value.
Using the function therefore is as simple as:

sub MAIN( Str $file-name ) {
    say readN( $file-name, 4 );
    say readN( $file-name, 4 );
    say readN( '/home/luca/.zshrc', 10 );

PWC 98 - Task 2

In the second task there was the need to search for a value in an ordered array of integers: if the value is found, the index has to be printed, otherwise the array has to be modified and the new element has to be inserted preserving the ordering.
I decided to implement the two branches by means of given. The easiest case is the one where there is a direct match: .grep can be used to find out a match, and we are interested in the very .first match found. In the other case, I need to search for the .first index that has a value greater or equal of the searched one, then a new array is composed by splitting the original one in two parts and by inserting the new value in the middle. Therefore it resolves as:

sub MAIN( *@values where { @values.grep: * ~~ Int } ) {
    my @N = @values[0 .. *-2 ];
    my $N = @values[ *-1 ];

    # get the index if the element is there
    given @N.grep( $N, :k ).first { .say && exit if $_ }

    # if here the key is not there, let's see where to insert
    given @N.grep( { $_ >= $N }, :k ).first {
        @N = |@N[ 0 .. $_ - 1 ], $N, |@N[ $_ .. * ];
        .say && exit;


Both the given branches print the index and exit, so there is no particular added value in modifying the array. Please note that, in the case a new value is inserted, the arrays slices are flatted by means of the | operator.
Thanks to the :k adverb of grep it is trivial to find out the index to operate on.

The article Perl Weekly Challenge 98: reading chars and inserting in array has been posted by Luca Ferrari on February 1, 2021