Perl Embedding

The next thing I wanted was the ability to dynamically load other Perl extensions such as the Tk extension, database extensions or anything else that might prove useful. This requires an xs_init function in place of the NULL in perl_parse as shown below.

perl_parse(MyPerl, xs_init, 2, my_argv, env);

To create the xs_init, I used the following code:

perl -MExtUtils::Embed -e xsinit -- -o - >xs_init.c

One of the first problems I ran into was the fact that Perl redefined yypars to be Perl_yypars. I fixed this by putting new #define statements around places where I used sc's yypars. This created a lot of compiler warnings, but did allow the code to compile correctly.

The other problem I encountered was with the SvIOK and SvNOK macros. These check an SV for a number or an integer, or more precisely, they check to see if the double-value portion of an SV is valid at that point in the code.

Originally, I had the SvIOK and SvNOK macros around any code to which I was expecting to send an integer. The problem is this will not accept code like the following,

sc_put_num_val("34.3"); # this is in perl

because it is being passed a string value and the number part of the SV was not valid at that time. The SvIV and SvNV macros will convert this to a number even if it is not a valid string. I was parsing strings from a file using regular expressions, and the value I would get in $1 would be a string, even though it was numeric. Once I realized SvNV would produce a number for me, my test script started working.

This example is not the cleanest implementation of embedding Perl into an application. It was meant as a quick solution to a problem. With an embedded Perl interpreter, sc is quite a bit more powerful than before. One example included with the source is a mortgage calculator that grabs the interest rates form the CNN Financial News web site. With all the Perl modules available, the possibilities are endless.

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