Octave-2-Matlab & Back (2)

Doxygen is such a nice tool. I cannot over emphasize its utility when trying to read a large codebase like GNU Octave's. So in trying to solve our parse-tree walker to convert Octave(Matlab) code to the other Matlab(Octave), we use the inheritance class list for GNU Octave Interpreter.

The following, is the class inheritance for the nodes on the parse-tree, that are in the AST. Now the interpreter or a conversion tool like Octave-2-Matlab will walk this tree. The AST Walker implements the visitor pattern supported by the tree object.



We can now look into the organization of the AST Walker, which is neatly documented/illustrated in this working piece of code at /cvs/octave/src/pt-pr-code.{cc|h}. This AST walker inherits from the base class as follows,

with tree_walker, a pure virtual base class, that encourages polymorphic design. Some of the members of tree_walker include

Now a debugger, code conversion tool, lint-like checker or whatever has to conveniently invoke the parser for the AST, and then walk it for whatever operations it needs to perform on the tree.

virtual void visit_index_expression (tree_index_expression &)=0
virtual void visit_matrix (tree_matrix &)=0
virtual void visit_cell (tree_cell &)=0
virtual void visit_multi_assignment (tree_multi_assignment &)=0
virtual void visit_no_op_command (tree_no_op_command &)=0
virtual void visit_constant (tree_constant &)=0
virtual void visit_fcn_handle (tree_fcn_handle &)=0
virtual void visit_parameter_list (tree_parameter_list &)=0

and many more functions that correspond to each language-object that derives from tree, and relevant functions that 'execute' that command or expression.

So the organization of all this code would start at the front end like:

   1 main
  2 begin
  3   AST=call-parser()
  4   cwalk=Code_Converting_Walker(OCT2MAT)
  5   cwalk.set_tree(AST)
  6   cwalk.visit()
  7   cleanup abracadabra  
  8 end

So that settles it all, if you know what to write within the pure virtual functions, visit_index_expression (tree_index_expression &)=0 and such. This conversion code is put simply in the previous blogpost by walking this tree in a post-order fashion.

Next time we could see how to write the Oct2Mat converter based on the parse tree, or atleast drive the tree-printer class code.

Cheers,
Muthu