Skip to main content

Learning Perl5i #3 revisted

I was somewhat uncomfortable that my solution to the combinatorics task, which involved a single, not very long routine, became so long with the addition of command line processing and POD  documentation. For one thing, while it had some information about how to invoke the routine, it did not have tests.

I still feel that a book on programming, say, should have a fully-implemented solution once a chapter, perhaps, to show the way things should be done. But that is too long for every single bit of code. Full documentation and sample implementations stretch on too long, compared to the few lines a snippet actually deserves.

Providing tests may still be appropriate. They take up less space than full documentation, yet explain how the various components work, by the very act of stress-testing those lines of code. Tests provide examples of how the code should be invoked.

Revising the combinatorics task into a module, this generates:

use perl5i::2;

# ----------------------------------------
# generate combinations of length $n consisting of characters
# from the sorted set @set, using each character once in a
# combination, with sorted strings in sorted order.
#
# Returns a list of array references, each containing one 
# combination.
#
func combine($n, @set) {
    return unless @set;
    return map { [ $_ ] } @set if $n == 1;

    my ($head) = shift @set;
    my @result = combine( $n-1, @set );
    for my $subarray ( @result ) {
$subarray->unshift( $head );
    }
    return ( @result, combine( $n, @set ) );
}

# ------------------------------------------------------------------
# Tests
#
func runtests() {
    eval { use Test::More }; # only include if testing

    test_no_set();
    test_length_zero();
    test_length_one();
    test_longer();
    done_testing();
}

func test_no_set() {
  is( combine( 1, () ), undef, 
      'set == empty list returns empty array' );
  is( combine( 1 ), undef, 
      'set not provided returns empty array' );
}

func test_length_zero() {
  is( combine( 0, 'a' ), undef, 'zero length returns empty array' );
}

func test_length_one() {
  my ( @results ) = combine( 1, 'a' );
  is_deeply( \@results, [['a']],
    'length 1 returns unary set as array element');

  @results = combine( 1, 'a', 'b', 'c' );
  is_deeply( \@results, [['a'], ['b'], ['c']],
    'length 1 returns larger set as array elements');
}
func test_longer() {
  my ( @results ) = combine( 2, 'a', 'b', 'c' );
  is_deeply( \@results, [['a', 'b'], ['a', 'c'], ['b', 'c']],
    'longer length generates list of  combinations');
}
# ------------------------------------------------------------------
# Run tests if invoked as a program, rather than in cluded as a 
# module.
#
runtests() unless caller();

Output from invoking the module as a program:

bash-3.2$ perl combinations.pli
ok 1 - set == empty list returns empty array
ok 2 - set not provided returns empty array
ok 3 - zero length returns empty array
ok 4 - length 1 returns unary set as array element
ok 5 - length 1 returns larger set as array elements
ok 6 - longer length generates list of  combinations
1..6

Comments

Popular posts from this blog

BASH Matrix Multiplication

tl;dr Bash is not the language for math-intensive operations. REPS=$1; FILE_1=$2; FILE_2=$3 OUTFILENAME=$4; readonly COLS=`head -1 $FILE_1 | wc -w`; readonly ROWS=`cat $FILE_1 | wc -l`; # echo "rows is $ROWS; cols is $COLS" if [[ $ROWS != $COLS ]]; then echo "Expecting square matrices, " \ "but rows = $ROWS, cols = $COLS\n"; exit 1; fi # -------------------------------------------------- # SUBROUTINES # function outputMatrix() { local matrixname=$1; local matrix; local elem; echo "matrix is '$matrixname'."; eval matrix=\( \${${matrixname}[@]} \); local i=0; for elem in "${matrix[@]}"; do echo -n "$elem "; if (( ++i == $COLS )); then echo ''; i=0; fi done } function multiply() { declare -a product; local M=$1 N=$2; local i j k idx1 idx2 idx3; for ((i=0; i < $ROWS; i++ )); do for ((j=0; j<$COLS; j++)); do

Perl5, Moxie and Enumurated Data Types

Moxie - a new object system for Perl5 Stevan Little created the Moose multiverse to upgrade the Perl 5 programming language's object-oriented system more in line with the wonderfull world of Perl 6. Unfortunately, it's grown into a bloated giant, which has inspired light-weight alternatives Moos, Moo, Mo, and others. Now he's trying to create a modern, efficient OO system that can become built into the language. I've seen a few of his presentations at YAPC (Yet Another Perl Conference, now known as TPC, The Perl Conference), among them ‎p5 mop final final v5 this is the last one i promise tar gz <. So I was delighted to recently see an announcement of the module Moxie, and decided to try implementing a card game. While the package provides some POD documentation about the main module, Moxie, it doesn't actually explain the enum package, Moxie::Enum. But delving into the tests directory reveals its secrets. Creating an Enum package Ranks { use

Creating Perl5 Objects with Moxie

Having in the previous article prepared data types for car suits and card ranks, I can now combine them to provide a playing card class, using Stevan Little's Moxie module (version 0.04, so definitely early days.) The goal is to provide an object-oriented paradigm to the Perl 5 programming language which is more sophisticated, more powerful and less verbose than manually bless() -ing hashes. To achieve that goal it needs to be faster and light-weight compared to Moose. Currently, Moxie.pm and and MOP.pm are add-on modules, but eventually, when they are more complete, when the wrinkles have been ironed out, and when they have gained acceptance and a community of users, they might be merged into the Perl core. One significant feature of Moxie is that it reduces boilerplate code. You don't have to specify warnigns or strict . As well, the features or the perl you are using are enabled, among them say , state , signatures , and post_deref . A Simple Moxie Class packag