Using ASTCreator Sample Clauses

Using ASTCreator. As a part of the Overture platform there is a tool called ASTCreator that is used to automatically generate the AST for all of the VDM dialects supported by Over- ture. This tool is also used to generate the AST for the CML dialect via its exten- sion feature, and it uses the VDM AST as its basis for the CML AST. This usage allows us to directly reuse much of the interpreter and typechecker source code from the Overture platform in the CML tool without needing to change the VDM typechecker or interpreter. The structure of a dialect is defined in an AST script that is read in by the ASTCre- ator tool. The ASTCreator tool then resolves the necessary structure of the target AST from this script and generates the Java class files that implement the AST, and in addition it provides a set of Java class files that implement the basic AST visitors within the correct Java packages. These visitors are used to manipulate the ASTs. To implement some functionality on the ASTs, they do not need to alter the base AST classes at all. Indeed, doing so is strongly discouraged. Instead, one of the visitor classes should be subclassed and the necessary functionality is imple- mented in this subclass. When the subclassed visitor is given to the visit method of the AST, the AST will, in turn, invoke a specially-named method in the sub- class for each node in the tree, passing that node as a parameter; each possible node in the AST has a separate method that is invoked in the visitor. This structure makes it possible for a visitor to act upon every element of an AST, and because it is the responsibility of each node-specific method to invoke the visitor for its children in the AST, it is also possible for the developer to control execution of the visitor over the structure of the AST. Each of the basic visitor classes implements a minimal version of a method for each possible node in the AST, for which the functionality of these methods is only to visit the node’s children. This allows the developer to subclass one of the basic visitor classes and only write the methods for the nodes of interest, rather than being required to implement every method for every possible node in the AST. Note that ASTCreator may also be used by plugin developers to create ASTs for other grammars that are translated to or from the CML AST.