A naïve db client in Perl 6

db-shell.p6

# a rewrite of http://blogs.perl.org/users/ovid/2016/01/a-naive-sql-shell.html in Perl 6
use v6;
use DBIish;
use Linenoise;
use Text::Table::Simple;

my constant HIST-FILE = '.myhist';
my constant HIST-LEN  = 100;
my constant ROW-LIMIT = 100;

linenoiseHistoryLoad(HIST-FILE);
linenoiseHistorySetMaxLen(HIST-LEN);

while get-query -> $query {
    my (@cols, @rows, $num-rows) := get-cols-and-rows-from-query($query);
    say lol2table(@cols, @rows).join("\n");

    say "Showing {ROW-LIMIT} out of $num-rows rows" if @rows < $num-rows;
    CATCH {
        say "Error executing query: $_", Backtrace.new.concise;
    }
}

linenoiseHistorySave(HIST-FILE);

sub get-query {
    my $query = '';
    while linenoise '?- ' -> $line {
        return if $line ~~ / \\q \s* $ / {
        $query ~= "$line\n";
        last if $line ~~ / ';' \s* $ /;
    }
    $query .= chomp;
    linenoiseHistoryAdd($query);
    return $query;
}

sub get-cols-and-rows-from-query (Str $query) {
    state $dbh = DBIish.connect: 'Pg', :database<...>, :user<...>, :RaiseError;
    
    my $sth = $dbh.prepare($query);
    $sth.execute;
    my @rows = $sth.allrows(:array-of-hash);
    $sth.finish;
    
    my $num-rows = @rows.elems;

    my @cols = @rows[0].keys;
    @rows .= map: *.values;
    @rows .= head(ROW-LIMIT) if @rows > ROW-LIMIT;
    
    return @cols, @rows, $num-rows;
}