[antlr-interest] CommonTree & Tree grammar versus DIY
Terence Parr
parrt at cs.usfca.edu
Thu Aug 21 13:26:48 PDT 2008
On Aug 21, 2008, at 1:20 PM, Andy Tripp wrote:
> Terence Parr wrote:
>
>> Yep. I'm now in favor of manipulating the text instead and
>> regenerating the AST for the altered position. Tree manipulation is
>> fraught with danger
>
> That seems to me like a very odd thing to say.
> Manipulating a tree data structure is inherently no more dangerous
> than
> manipulating any other kind of data structure.
Apparently you've never made a cycle in a tree before ;) Recursive/
self-similar data structures *ARE* more difficult to alter properly
than a List; by hand anyway. For lang X to X, morphing trees is ok
but altering language makes each new pass have to match a new kind of
tree. lang X to Y is not so good as a result.
> Now imagine the same program working on a tree rather than a list.
> Same situation: the program changes the shape of the tree lots of
> times in lots of ways, and
> having to specify the "shape" of it after every change would be silly.
> That's the situation when trying to use treewalkers in a translator.
> It's just that the silliness isn't apparent until you get beyond
> just a couple of valid tree "shapes".
That's why I said I am liking the text rewrite approach; the approach
you are using, no?
Ter
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