Web Log

I’ve Just pushed Chapter 17 live. There’s a problem currently with the [download] button for the Perl examples. I’ve been battling with my hosts to see if there’s any way to turn off cgi handlers for the .pl files in the examples directory. The standard .htaccess hacks don’t seem to work. So giving up on that, I thought “why not make the .pl files cgi scripts that return the content?” So I did that, but even though the resulting scripts seem to work fine when executed locally on the cli, the server still throws an error (no code provided.) So I’m probably going to have to choose a different extension for all the examples, like .ex or .eg in order to get it all to work.

Bit of a delay getting chapter 17 out, mainly because I’m in the process of applying for a new job (C++) but also because one of the tests for the new chapter (the classic Prolog “append” definition) is screaming out for dotted pair notation, which is best introduced way back in version 0.0.5 of the interpreter in chapter 8, so I have to add those features there, then roll forward the changes through the rest of the code. That roll forward is itself complete, but I have to go through each intermediate chapter and make sure the discussion of the amended code is complete. Please bear with me.

This chapter will cover pattern matching and Unification, add unify as a built in primitive, then use it along with amb from the previous chapter to implement a real logic-programming system in PScheme. I’m really pleased with how this has panned out, when I started the book I put up a list of topics that I would like to cover, but honestly didn’t have the nerve to suggest that I might get as far as this. But as it happens the polymorphism of the basic scheme datatypes has made it a breeze.
Of course as usual the text of the book is not so good, I seem to be forgetting how to write (and even how to spell) as I get older.

I guess the main reason I wanted to start a blog was to give people a place to pass comments on the book. Writing can be a thankless task and although a kind few people have gotten back to me with encouraging comments, it would be much nicer if I could gather all those comments into one place. So feel free to comment.

Testing!