[antlr-interest] Skipping AST nodes in tree-parsing

[Arnar Birgisson]

Hello..

Thanks for the lightning fast response :o)

This works, I have:

funcdef
  : #("function" ID arg_list (block_stmt)=> block:.)
  ;

This ensures that the atom is of the correct token.

One thought this leads to: what meaning does ! have in tree parsers?
Excpecting to match a token and create the AST for it but skip
descending
into it, I first tried

funcdef
  : #("function" ID arg_list block_stmt!)
  ;

which was accepted by ANTLR but generated the exact same code as it did
without the !.

Arnar

> -----Original Message-----
> From: mzukowski at yci.com [mailto:mzukowski at yci.com] 
> Sent: 22. september 2003 18:35
> To: antlr-interest at yahoogroups.com
> Subject: RE: [antlr-interest] Skipping AST nodes in tree-parsing
> 
> 
> funcdef
>   : #("function" ID arg_list .)
>   ;
> 
> '.' is a wild card and just matches one node but does not 
> decend into the
> tree, just like ID above does not descend into a tree and 
> just matches one
> node of type ID.
> 
> Monty
> 
> -----Original Message-----
> From: Arnar Birgisson [mailto:arnarb at oddi.is] 
> Sent: Monday, September 22, 2003 11:30 AM
> To: antlr-interest at yahoogroups.com
> Subject: [antlr-interest] Skipping AST nodes in tree-parsing
> 
> 
> Hello there.. 
> 
> Is there a way in a treeparser to skip the walking/parsing of 
> a tree node? I
> want to store a reference to the AST instead. Two examples: 
> 
> This is in my parser: 
> 
> funcdef
>   : "function"^ ID LPAREN! arg_list RPAREN! block_stmt
>   ;
> 
> and in the tree parser: 
> funcdef
>   : #("function" ID arg_list block_stmt)
>   ;
> 
> Now, instead of parsing ID, arg_list and then block_stmt 
> nodes, I only want
> to parse the ID and arg_list and skip over block_stmt, 
> instead I will store
> a reference to the node in a hashtable indexed on the given ID. 
> 
> Later, when the function is called in the user-program, the 
> tree-parser rule
> for a function call will look up the AST for the function 
> definition by its
> name and manually call appropriate rule for walkin the AST, 
> after installing
> the given paremeters into the symbol table. 
> 
> Another example of this is rewriting for loops to while loops: 
> 
> for (stmt1; expr; stmt2) stmt3; 
> 
> becomes 
> 
> stmt1; while (expr) { stmt3; stmt2; } 
> 
> This involves the reordering of the atoms, i.e. this 
> translation scheme is
> not simple by the definiton of the Dragonbook. 
> 
> How does one do this kind of translation in a tree walker? 
> Perhaps someone
> could point out a simpler solution, but if one could skip 
> over nodes as
> described above and manually call the parsing method for them 
> at a later
> time, this becomes trivial. 
> 
> Arnar
> 
> 
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