Package Organization

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Package Organization

Linguist comprises a highly-organized set of Java 1.1 classes, all of which are provided as Java source for you to use as the starting point for your own productions. The standard language packages implement the language features as we supply them. Here is a list of the more common ones; the distribution may well include others.:

basicdatagraphicsmedia
servlet

Here are the major features of each package:

The basic package contains all of the keyword handlers for the basic language features, as documented in the Reference. The package contains a number of standard classes for processing condition and value and for handling errors, and below this are five sub-packages:

conditionhandlerkeywordruntimevalue

The condition sub-package contains run-time handlers for conditional expressions. Suppose your script has the line

if X is greater than 25 stop

The compiler handler for the if keyword scans the variable X, then looks for a conditional expression, in this case is greater than. It has no methods of its own for processing conditions, so it asks basic.BLGetCondition to process the condition and return a suitable handler if it can. This particular condition is part of the basic package, so a handler from the basic.condition sub-package is returned. (The use of handlers is fundamental to the operation of Linguist, so it will be explained many times in different ways. Don't worry if it's not clear now.)

The handler sub-package contains run-time handlers for each feature of the script language. When the compiler has finished parsing a feature it creates a handler, which is your own derivative of a standard Java class provided by us. The handlers are placed into an array; this becomes the program itself. Each handler has constructor and execution methods, so the overhead in running a script is low.

The keyword sub-package contains the classes that actually do most of the script compilation. This is the key to the way Linguist works. Because these classes are under your control, rather than being buried in a monolithic compiler, you can safely make changes to and extend the syntax of your script language.

The runtime sub-package contains miscellaneous classes such as a background handler for the package and a class that contains error messages which may need to be translated to another language.

The value sub-package has a similar purpose to condition. It handles any value that your script requires. Those in the basic package deal with numeric and string values, that is, anything that translate to a number or a string. So left 4 of Line is a string value, while the length of Line is numeric. (Both examples assume Line to be a string buffer).

The data package provides a set of features that embody the major functionality of JDBC, providing access to SQL databases. See the Reference for a description of each command handled. It contains the same sub-packages as basic, so the same general notes apply.

The graphics package provides a set of features that embody part of the Swing graphics libraries. See the Reference for a description of each command handled. It contains the same sub-packages as basic, so the same general notes apply.

The media package provides wrappers for JMF, the Java Media Framework, allowing your scripts to manage sound and video. See the Reference for a description of each command handled. Note: Only systems that have a port of the Java Media Framework can use the media package..

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