Brian Wisti

Last night I reached chapter 4 of Think Python, which is full of good old fashioned turtle graphics stuff.

It’s just - well - there’s a problem. I don’t think there is a port of the swampy library to Perl 6. I could write one, but that would probably require a Tk interface with Perl 6. Even just writing a Perl 5 Tk version of Swampy is beyond my spare time attention span.

I know what I’ll do. I’ll cheat and have perl6 call python.

First, I install Swampy. It is available on PyPi;

$ tar xfvz swampy-2.1.1.tar.gz
$ cd swampy
$ python setup.py build
$ sudo python setup.py install

If you didn’t break your pip like I did the other day, you can probably just pip install swampy.

Right now I’m just shooting for enough to make the first example work. fd and lt need to be implemented, and nothing else.

use v6;

my $turtle = 'turtle';
my @directives;

sub fd($distance) {
    @directives.push("fd($turtle, $distance)");
}

sub lt() {
    @directives.push("lt($turtle)");
}

sub swampy() {
    my $code = @directives.join("\n");

    my $full-code = qq:to/END/;
from swampy.TurtleWorld import *

world = TurtleWorld()
$turtle = Turtle()

$code

wait_for_user()
END

    my $python-file = save-code $full-code;
    say "Python code is in $python-file";
    run-python-with $python-file;
}

sub save-code($code, $name='default.py') {
    my $handle = open $name, :w;
    $handle.say($code);
    $handle.close;

    return $name;
}

sub run-python-with($script) {
    my $python = qx{which python}.chomp;
    my $result = qqx{$python $script}.chomp;

    if $result {
        say "$python output:";
        say $result;
    }
}

fd(100);
lt();
fd(100);
swampy();

Total cheat. I do one-for-one generation of Python Swampy directives from Perl 6, and when everything is generated I create a Python file and hand that off to python. Despite my good intentions of looking for the default Python interpreter, the odds are good that this will only work on my machine.

Even so, I need to make this a module. I don’t want to copy and paste all this every time I want to work through a Swampy example in the book. I’m sticking with a module interface rather than a class so that I can keep the invocation style used in this chapter of Think Python. Also, I’m not entirely certain that I am ready for Perl 6 classes quite yet. Maybe later.

Rather than bore you with details, I’ll send the patient reader to perl6-swampy. This is a simple stupid Perl 6 module that can be downloaded, and then installed with Panda. It probably won’t stay simple for long, but let’s hope it stays stupid. I’m no good with code that’s smarter than I am.

And then the starter code for Chapter 4?

use v6;

use Swampy;

fd(100);
lt();
fd(100);

draw-it();

Yes, I have grand ideas for Swampy.pm6, including crazy stuff like documention. And actual functionality. But hey. It works. I can draw a line and turn left, but in Perl 6. Yay me!

All I had to do was cheat.