[antlr-interest] advocacy of C++ support in ANTLR 3.x

[Tomas Potrusil]

I was wrong. I do not need to "override" a tree, but a tree adaptor!
Investigating the mailing-list and the source code I've found that the
generated parser uses just the adapter and not the tree directly. But then
there is something strange in the current C runtime:

 

In Java runtime the tree adaptor interface works with "Object" objects only.
Of course it must abstract access to real tree nodes - it is an adaptor; not
just an object factory.  Terence Parr in a documentation says: "Rather than
have a separate factory and adaptor, I've merged them."

 

The C runtime simulates its Java version, but it doesn't work with void*
("Object" in C) but directly with ANTLR3_BASE_TREE. It is not an adaptor
anymore, it is just an object factory. Methods like

ANTLR3_TREE_ADAPTOR::addChild(...adaptor, pANTLR3_BASE_TREE t,
pANTLR3_BASE_TREE child)

are useless, because everyone can call t->addChild(child) directly.

 

This prevents me to use our existing AST C++ classes within ANTLR without
"subclassing" them from ANTLR3_COMMON_TREE, doesn't it.

 

Tom

 

From: antlr-interest-bounces at antlr.org
[mailto:antlr-interest-bounces at antlr.org] On Behalf Of Jim Idle
Sent: Monday, March 31, 2008 1:39 AM
To: ANTLR
Subject: Re: [antlr-interest] advocacy of C++ support in ANTLR 3.x

 

You will probably find it best to override pANTLR3_COMMON_TREE by
encapsulating this within your own structure, as per the docs. This, as all
the structures are, is a set of pointers to functions and you need only
override the ones that you have to, just as in Java. Runtime type checking
'can' be an overhead, so i am not sure you would want to do that anyway, but
I will contemplate your suggestion of course as it has some merit.

 

Jim

 

From: Tomas Potrusil [mailto:potrto at centrum.cz] 
Sent: Friday, March 28, 2008 5:43 AM
To: Jim Idle
Cc: ANTLR
Subject: RE: [antlr-interest] advocacy of C++ support in ANTLR 3.x

 

Oh yes, I know. I've already made a prototype implementation of a part of
the grammar based on the idea I presented bellow (atom returns [OurNode*
result] etc.). It is working but it is a little bit clumsy and I cannot use
the resulting AST for a tree parsing - of course, I'm creating my own AST.

 

I've been thinking about the new tree adapter (I was talking about bellow)
and probably you are true,  few C++ wrappers could do the work. But there is
one inconvenience - there is not an "abstract" tree yet. The most abstract
tree is ANTLR3_BASE_TREE_struct which contains children vector and other
attributes. The ANTLR3_TREE_struct with only pointers to functions
(something like a Java interface) would suit my needs better. Our existing
AST nodes solve the storage already. Could you do it, please?

 

Another problem is safety. When somebody call
ANTLR3_BASE_TREE_struct::addChild(pANTLR3_BASE_TREE tree) for example, I
must trust him that the tree argument is really the tree he is calling. I
cannot write dynamic_cast<MyTreeWrapper>(tree->super). This cannot be solved
in the current C-based system.

 

Tom

 

From: Jim Idle

 

ANTLR 3.1 C target can now incorporate C++ code directly into the grammar
and so can easily call your existing C++ code. All you do is compile the C
output file as C++ (or rename it to .cpp perhaps). 

Can you try using that and let me know if you think that there is anything
that you could do if the runtime was C++ that you can't do right now? I
don't really think that there will be.

You need to get the latest 3.1 snapshot from the downloads page and use the
ANTLR Tool hjar in there. Then build the ANTLR 3.1 C runtime from the tar.gz
in the dist director under the runtime/C directory in the snapshot. 3 or 4
people have successfully integrated their C++ code with the C target now and
I think you will have similar success :-)

Jim

 

-----

Hallo,

 

I'm new to the list. I'm trying to use ANTLR for generating a SQL parser
because our current parser doesn't support Unicode input - it was generated
by Lex/Yacc. We use C++ and we have our own complex AST that is used by a
SQL engine already... So my idea is to write a tree adapter that would
create our existing AST nodes (they would just inherit ANTLR tree
interface).

 

And here comes a problem that ANTLR 3.x doesn't contain support for "pure"
C++ implementation. I've just found Jim Idle's "promise":

 

> Later I may well produce a complete C++ implementation from scratch,

> however, at this point I am not sure that it buys you anything. Please

> let me know if there are things you cannot do with the system as it

> stands (other than access the tokens and so on using C++ objects, which

> will be done later). 

 

I know that the problem could be solved with the current system somehow, but
it would be probably very ugly. So yes, complete C++ implementation will buy
us something! Or we can use ANTLR 2.x.

 

Right now we will probably try to build the AST by hand:

 

atom returns [OurNode* result]

@init { $result = NULL; }

:              NUMBER

                {

                               std::string str((char*)$NUMBER.text->chars,
$NUMBER.text->len);

                               $result = new OurNumberNode(str);

                };

 

Or do you have some other ideas?

 

Thanks

 

Tom

 

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