3.2 The Smalltalk-in-Smalltalk library

The Smalltalk-in-Smalltalk library is a set of classes for looking at Smalltalk code, constructing models of Smalltalk classes that can later be created for real, analyzing and performing changes to the image, finding smelly code and automatically doing repetitive changes. This package incredibly enhances the reflective capabilities of Smalltalk.

A fundamental part of the system is the recursive-descent parser which creates parse nodes in the form of instances of subclasses of RBProgramNode.

The parser’s extreme flexibility can be exploited in three ways, all of which are demonstrated by source code available in the distribution:

• First, actions are not hard-coded in the parser itself: the parser creates a parse tree, then hands it to methods in RBParser that can be overridden in different RBParser subclasses. This is done by the compiler itself, in which a subclass of RBParser (class STFileInParser) hands the parse trees to the STCompiler class.
• Second, an implementation of the “visitor” pattern is provided to help in dealing with parse trees created along the way; this approach is demonstrated by the Smalltalk code pretty-printer in class RBFormatter, by the syntax highlighting engine included with the browser, and by the compiler.
• The parser is able to perform complex tree searches and rewrites, through the ParseTreeSearcher and ParseTreeRewriter classes.

In addition, two applications were created on top of this library which are specific to GNU Smalltalk. The first is a compiler for Smalltalk methods written in Smalltalk itself, whose source code provides good insights into the GNU Smalltalk virtual machine.

The second is the automatic documentation extractor. gst-doc is able to create documentation even if the library cannot be loaded (for example, if loading it requires a running X server). To do so it uses STClassLoader from the Parser package to load and interpret Smalltalk source code, creating objects for the classes and methods being read in; then, polymorphism allows one to treat these exactly like usual classes.