[antlr-interest] antlr v4 wish list

[Terence Parr]

added

* Tree parser error handling should skip subtrees not nodes; these are programming errors not input errors.  The flat stream makes it hard to resync.

Ter
On Mar 24, 2011, at 2:07 AM, Iztok Kavkler wrote:

>> Howdy, I'm going to start augmenting ANTLR v3 significantly to create v4. The goal is backward compatibility; any new functionality, of course, will require altering or augmenting your grammars to take advantage of it. Here is my potential list of updates:
>> 
>> http://www.antlr.org/wiki/display/ANTLR4/ANTLR+v4+Wish+list
>> 
>> Anything to add or comment on?
>> 
>> Ter
>> 
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> 
> A new error recovery mode for tree parsing:
> When parsing ASTs, the ordinary error recovery strategies based on token 
> deletion/insertion are completely useless, because there are no man-made 
> syntax errors. In my experience, what you really want to do is the 
> following: assume that you have an error handler attached to some rule 
> and an error happens somewhere in the subtree of the node parsed by that 
> rule. When the handler catches an error, the parser must skip the 
> remainder of that subtree, otherwise the parser position is not 
> consistent with the grammar position anymore. In AST implementations 
> that are based on pointers between nodes this happens automatically, but 
> Antlr's representation as a flat list of nodes with UP and DOWN tokens 
> makes it requires some work - the parser has to keep track of the 
> current node's depth and skip the appropriate number of UP nodes 
> whenever an error is caught.
> 
> Iztok
> 
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