Including files and hidden tasks

File inclusion within PHP can really work on your nerves. I can remember an occasion when it took me about an hour to find out why a file was not included. This was because PHP first looks in the working-directory and then in the current directory. If there is a file with the same name in both directories the first one is included. If I had taken a look at the documentation then this would not have come as a surprise to me.

Way this paragraph about including files? Because this feature is added to php-front. There is now a strategy available that uses the 'require' and 'include' statements within a PHP-file to find and parse other PHP-files. These PHP-files are added to the environment and can be accessed anywhere in the traversal.

The implementation of this inclusion strategy included the modeling of the different paths that PHP used. As mentioned above, PHP uses two different directories to search for files. The working directory, where the process was initiated, and the current directory, where the current file resides. These directories are the same if there is only one file to be processed.

I did not want to mess with the current-directory of the tool when including files, so the paths are kept internally. This requires some string manipulation to make up the right include-path, but it works. By keeping track of the include-path and working-directory within the application there is even support for the functions ini-set and chdir!

All this could not have been done without moving things around and adding some small but useful strategies. This included: a separate section is added to the library that holds common strategies, the parsing is moved to the library and the environment can now store complete AST's. All of these things are small and easily done. But unfortunately, many small things take up a lot of time.

The mechanism of including files can be improved by adding partial evaluation of PHP-code to the library. This will add annotations with known values to terms. By using this, and some constant-propagation, the following will succeed:

<?php
    $path = './some/path/';

    require_once $path.'filename.php';
?> 

This is commonly used within projects so this should be supported. So on to the simple evaluation and constant-propagation!