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antlrgrammarabstract-syntax-treeantlrworks

ANTLR ignoring AST operators

I am using the ^ and ! operators to set the root node and to not not be included in the AST, respectively. However, it is not making a difference in the tree that is generated by ANTLRWorks. So I am not sure if my grammar is incorrect or if ANTLRWorks just isn't creating a correct tree.

Here is an snippet of my grammar

expr
:   '('! logExpr ')'!;

These parenthesis should not be included in the AST.

addExpr
:   multExpr ( (PLUS|MINUS)^ multExpr )*;

The PLUS or MINUS should be the root node in the AST.

However neither of these things are happening the way I expect them to. It makes no difference when I remove them or put them back. ANTLRWorks 1.4.3 ANTLR 3.4

Solution

  • ANTLRWorks' interpreter shows the parse tree, even though you've put output=AST; in the grammar's options-block, as you already found yourself.

    However, ANTLRWorks' debugger does show the AST. To activate the debugger, press CTL+D or select Run->Debug from the menu bar.

    The debugger is able to visualize the parse tree and AST. Note that it will not handle embedded code other than Java.

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