I just released to CPAN a distribution named Acme-Roman
(It's propagating yet, so maybe you can't reach immediately from your
favourite CPAN mirror.) As an
Acme module, it is a simple experience to allow using roman
numerals in Perl programs in a straightforward manner.
print I + II; # III, as expected
That was done with a bit of overload, AUTOLOAD and a part which
I am not satisfied with.
Some digression first. The idea came to me a long time ago
from the solution to a Ruby quiz, namely
Ruby Quiz - Roman Numerals (#22)
(See the hightlighted solution at the Quiz Summary in the same page.)
The trick in Ruby was done by defining strategic methods method_missing
(which is kind of Perl AUTOLOAD
) and const_missing
The Perl solution was quite natural, and I got to the point where
print I() + II(); # III
worked fine. But when I left the parentheses, it
only barfed at me with
$ perl -w -Ilib -MAcme::Roman -e 'my $x = I+II'
Argument "II" isn't numeric in addition (+) at -e line 1.
Argument "I" isn't numeric in addition (+) at -e line 1.
$ perl -w -Ilib -MAcme::Roman -e 'print I+II'
Name "main::I" used only once: possible typo at -e line 1.
print() on unopened filehandle I at -e line 1.
which revealed the barewords were not resolved with the provided
. I learned that if I provided an empty protoype
it worked. And that's how I coded -- but that kind of sucks:
I need to define the prototype of 3999 subs (I .. MMMCMXCIX)
to make it work. I think that's too expensive. (Who would like
to play with an Acme module which is as heavy as a useful module?
The Ruby solution is helped by the availability of
const_missing method functionality. The equivalent in Perl would
be to overload barewords, but overload documentation says:
Barewords are not covered by overloaded string constants.
Does anyone have any suggestion to make this lazier?
Or a different way to implement that?