[antlr-interest] Tree building limitation in tree grammars?

[franck102]

My parser grammar can generate a number of subtrees with similar structure,
and just a different root type. In the tree grammar I am trying to just pass
such a subtree along without any changes, but that is turning out to be much
trickier than I expected, am I missing something?

Given this AST: ^( AND true false ) I want the tree grammar to generate the
same AST subtree.

The following attempts are not working:

^( ( AND | OR ) booleanExpression booleanExpression )  // no rewrite =>
flattens the tree, 
                                                                           
// I get a nil root and 3 children

^( ( root=AND | root=OR ) booleanExpression booleanExpression )
-> ( ( AND | OR ) booleanExpression booleanExpression )               //
syntax error

^( ( root=AND | root=OR ) booleanExpression booleanExpression )
-> ( AND? OR? booleanExpression booleanExpression )                   //
syntax error

^( root=(AND | OR ) booleanExpression booleanExpression )
-> ( $root booleanExpression booleanExpression )                 // runtime
error, $root is empty

Am I going to have to split those rules??

Any suggestion appreciated!


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