Re: xml as intermediate representation

Hi


From: "tanuj" <khurana.tanuj@gmail.com>
> I am writing a compiler as a part of my course project and wanted to
> use xml as an intermediate representation language.All the coding is
> being done in C. Can u suggest me how to go about it.It would be great
> if u could mention some online resources available.
>
> Regards
> Tanuj
> [XML is a general purpose framework that can represent anything. A
> more relevant question is if someone's defined a DTD for this purpose
> and written tools to do interesting things with it. -John]


There are internal and external representations of abstract syntax
tree. External representation is used for long-time storing of AST -
for example, to pass it between different tools (such as parser and
semantic analyzer). And I agree that XML with proper DTD is very good
choice for this task because allows to use exisintg tools.


But internal representation of AST (when parser and other parts of
compiler/translator are in one process) needs to be data structures of
implementation programming language. XML provides universal DOM tree.
It is excessive implementation when you need to represent only
particular class of trees. For example, it seems more convenient to
have


struct IfStmt
{
        Expr* condition;
        Stmt* thenStmt;
        Stmt* elseStmt;
}


and use it as


IfStmt* if_node;
process( if_node->condition );


then


struct Node
{
        Node** children;
}


Node* node;
process( node->children[0] );


or even


process( condition( node ) );
Node* condition( Node* if_node ) { return node->children[0]; }


It is usual heterogenous vs homogenous trees problem and I suggest to
use homogenous trees only in cases when tree structure is defined
dynamically (as in XML tools).


Heterogenous tree also can provide homogenous interface.


So, I think that better solution for internal representation
of AST (intermediate representation) is heterogenous tree structure
generated from DTD or equivalent tree structure description.


This tree structure description also can be used as a documentation of
used tree structure. It is important when there are more than one
developer.


There are several tools offering notations for tree structure description.
I can mention some tools that can generate C code:
Zephyr's ASDL http://www.cs.virginia.edu/zephyr/asdl.html
Cocktail's AST http://www.cocolab.com/en/cocktail.html#Ast
TreeCC http://www.southern-storm.com.au/treecc.html


My own tool TreeDL http://treedl.sourceforge.net now can generate only
Java and C# code. But it has one important advantage: you can write
your own plugin that will generate whatever you want. It is useful
when you need custom tree walker, visitor, tree read/write routines or
something else that can be automatically generated from tree structure
description.


Regards,
Alexey


-----
Alexey Demakov
TreeDL: Tree Description Language: http://treedl.sourceforge.net
RedVerst Group: http://www.unitesk.com

Return to the comp.compilers page.
Search the comp.compilers archives again.