RogerBW's Blog

Perl Weekly Challenge 29 11 October 2019

I've been doing the Perl Weekly Challenges. This one dealt with expanding braces and calling C functions.

Write a script to demonstrate brace expansion. For example, script would take command line argument Perl {Daily,Weekly,Monthly,Yearly} Challenge and should expand it and print like below:

Perl Daily Challenge

Perl Weekly Challenge

Perl Monthly Challenge

Perl Yearly Challenge

Of course, there might be multiple braces in a single input, for example {Perl,Postscript} {Daily,Weekly,Monthly,Yearly} Challenge. In this case I feel it's appropriate to go through each of them separately, so that in this case the output would be eight lines.

First, I break down the input to find braced sections. These are turned into array references within @e. %r holds the maximum value for each variable section (i.e. number of alternatives minus 1). Non-variable sections remain as plain text in @e.

foreach my $text (@ARGV) {
  my %r;
  my @e=split /(\{.*?\})/,$text;
  foreach my $i (0..$#e) {
    if ($e[$i] =~ /^\{(.*)\}$/) {
      my @b=split ',',$1;

Set the accumulators to 0. We will iterate through each valid combination.

  my %a=map {$_ => 0} keys %r;
  while (1) {

First, produce the current output, choosing the appropriate alternative for each variable section. (If there are no variable sections, this will still work.)

    my @out;
    foreach my $k (0..$#e) {
      if (exists $r{$k}) {
        push @out,$e[$k][$a{$k}];
      } else {
        push @out,$e[$k];
    print join('',@out),"\n";

Generate a list of the indices of the variable sections. If there aren't any, our job is done and we can exit now.

    my @kl=sort keys %a;
    unless (@kl) {

Increment the first accumulator. If it's exceeded its maximum value, reset it and go on to the next one. If we run out of accumulators, we've finished.

    my $i=0;
    while (1) {
      if ($a{$kl[$i]} > $r{$kl[$i]}) {
        if ($i > $#kl) {
          last OUTER;
      } else {

I didn't do this in Perl6, because I'm still getting the hang of how complex data structures work there.

Write a script to demonstrate calling a C function. It could be any user defined or standard C function.

This is notoriously fiddly in Perl (not to mention that all the easily-found examples assume you'll be writing your own C functions, not using an existing library), but I ended up finding a nice simple module to do it.

use FFI::Raw;

my $cpf=FFI::Raw->new('','printf',

$cpf->call("%s\n",'a string passed from perl5');

This is something that Perl6 seems to have got right:

use NativeCall;

our sub cpf(Str, Str --> int32) is native(sub{''}) is symbol('printf') { * }

cpf("%s\n",'a string passed from perl6');

Comments on this post are now closed. If you have particular grounds for adding a late comment, comment on a more recent post quoting the URL of this one.

Tags 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s 3d printing action advent of code aeronautics aikakirja anecdote animation anime army astronomy audio audio tech aviation base commerce battletech beer boardgaming book of the week bookmonth chain of command children chris chronicle church of no redeeming virtues cold war comedy computing contemporary cornish smuggler cosmic encounter coup covid-19 crime crystal cthulhu eternal cycling dead of winter doctor who documentary drama driving drone ecchi economics en garde espionage essen 2015 essen 2016 essen 2017 essen 2018 essen 2019 essen 2022 essen 2023 existential risk falklands war fandom fanfic fantasy feminism film firefly first world war flash point flight simulation food garmin drive gazebo genesys geocaching geodata gin gkp gurps gurps 101 gus harpoon historical history horror hugo 2014 hugo 2015 hugo 2016 hugo 2017 hugo 2018 hugo 2019 hugo 2020 hugo 2021 hugo 2022 hugo 2023 hugo 2024 hugo-nebula reread in brief avoid instrumented life javascript julian simpson julie enfield kickstarter kotlin learn to play leaving earth linux liquor lovecraftiana lua mecha men with beards mpd museum music mystery naval noir non-fiction one for the brow opera parody paul temple perl perl weekly challenge photography podcast politics postscript powers prediction privacy project woolsack pyracantha python quantum rail raku ranting raspberry pi reading reading boardgames social real life restaurant reviews romance rpg a day rpgs ruby rust scala science fiction scythe second world war security shipwreck simutrans smartphone south atlantic war squaddies stationery steampunk stuarts suburbia superheroes suspense television the resistance the weekly challenge thirsty meeples thriller tin soldier torg toys trailers travel type 26 type 31 type 45 vietnam war war wargaming weather wives and sweethearts writing about writing x-wing young adult
Special All book reviews, All film reviews
Produced by aikakirja v0.1