[antlr-interest] wildcard in tree grammar

[Gavin Lambert]

At 09:14 27/11/2008, Oliver Zeigermann wrote:
 >Too bad for me as I have this in a tree parser (rule is spelled
 >with 3xe on purpose):
 >
 >treee
 >       : ^(. treee* )
 >       ;
 >
 >which will never come to see the "treee*" part as the first "."
 >matches the complete subtree making my analysis (code is left 
out
 >for clarity) defunct.
 >
 >Or am I missing something here (as usual).

I'm not sure how Ter ended up implementing it, but I don't think 
there should be any problem with what you have here.

A wildcard in the 'root' position can only be a single node, 
because you can't have a subtree as a root.  So the meaning of the 
above shouldn't have changed.

Although incidentally, I would expect the above to fail to match 
if you have anything other than subtrees; ie. while it should 
match this:

   ^(FOO ^(BAR ^(BAZ)) ^(WIBBLE))

I would expect it to fail to match this:

   ^(FOO ^(BAR BAZ) WIBBLE)