Perl5 -> Perl6: a file into an array

One of the most common task I find in my Perl programs is to read data from text files, and more often that what I would expect, I need to slurp the file (read all the lines at once). Well, to be more precise, I need to read all content into an array (while slurping is to read all the content into a scalar). In Perl 5 I tend to use the following snippet:

 my @headers;
 if ( @ARGV > 1 ){
     open my $tag, "<", $ARGV[ 1 ]   || die "\nError\n";
     local $/ = "\r\n";
     chomp( @headers = <$tag> );
     unshift @headers, '#NUM' if ( @headers );
     close $tag;
 }

The idea is as simple as:

define the @headers empty list;
check if the name of the file to read has been passed as argument;
open such file;
change the input field separator (DOS mode), not always required;
read all lines into @header and clean each line;
place other piece of data into the array;
close the file handle.

In Perl 6 the above reduces as:

 my @headers;
 if ( $file_tag.defined ) {
     @headers = $file_tag.IO.lines( :chomp );
     @headers.unshift( '#NUM' ) if ( @headers );
 }

First of all, using the named parameters to the MAIN function I do not have to check for the arity of arguments, but can check on the argument itself (in this case $file_tag). The lines method allows to get all the content at once, or well, lazyly, but since assigning a Seq to an array reifies it, it works as reading all the file and putting the lines into the array without any risk of leaving a pending file handle or missing any line. It is interesting to note that the lines method allows a boolean attribute, chomp to perform the clean up of each line. Since the method delegates to IO::Handle.lines, and since by default the latter uses both "\n" and "\r\n" to clean up lines, all the magic is done for me. Most notably, the chomp attribute is true by default, so I would have not declared it at all! The remaining is quite obvious.`

The article Perl5 -> Perl6: a file into an array has been posted by Luca Ferrari on September 19, 2017

Tags: perl6 , perl5 , programming