Question

I have a grammar which parses dot notion expressions like this:
a.b.c

memberExpression returns [Expression value]
  : i=ID                                     { $value = ParameterExpression($i.value); }
    ('.' m=memberExpression                  { $value = MemberExpression($m.value, $i.value); }
    )*     
  ;

This parses expressions fine and gives me a tree structure like this:

MemberExpression(
   MemberExpression(
     ParameterExpression("c"),
     "b"
   )
   , "a"
)

But my problem is that I want a tree that looks like this:

MemberExpression(
   MemberExpression(
     ParameterExpression("a"),
     "b"
   )
   , "c"
)

for the same expression “a.b.c”

How can I achieve this?

Answer 1

You could do this by collecting all tokens in a java.util.List using ANTLR’s convenience += operator and create the desired tree using a custom method in your @parser::members section:

// grammar def ...

// options ...

@parser::members {
  private Expression customTree(List tks) {
    // `tks` is a java.util.List containing `CommonToken` objects
  }
}

// parser ...

memberExpression returns [Expression value]
  :  ids+=ID ('.' ids+=ID)* { $value = customTree($ids); }
  ;