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    <p>I don't think there's an easy way to do that. You could make your rule like this:</p> <pre><code>function : ID PERIOD function -&gt; ^(function ID) | ID ; </code></pre> <p>but that only makes the last node the root and all other nodes its children. For example, the following source:</p> <pre><code>a.b.c.d.e </code></pre> <p>will result in the following tree:</p> <pre><code> e / / \ \ d c b a </code></pre> <p>I can't see an easy fix since when you first parse <code>a.b.c.d.e</code>, <code>a</code> will be the <code>ID</code> and <code>b.c.d.e</code> the recursive call to <code>function</code>:</p> <pre><code>a.b.c.d.e | +-----+ | | | `-----&gt; function | `----------&gt; ID </code></pre> <p>resulting in the fact that <code>b.c.d.e</code> will have <code>a</code> as its child. When then <code>b</code> becomes the <code>ID</code>, it too is added as a child next to <code>a</code>. In your case, <code>a</code> should be removed as a child and then added to the list of <code>b</code>'s children. But AFAIK, that is not possible in ANLTR (at least, not in a clean way inside the grammar).</p> <hr> <p><strong>EDIT</strong></p> <p>Okay, as a work-around I had something elegant in mind, but that didn't work as I had hoped. So, as a less elegant solution, you could match the <code>last</code> node as the root in your rewrite rule:</p> <pre><code>function : (id '.')* last=id -&gt; ^($last) ; </code></pre> <p>and then collect all possible preceding nodes (<code>children</code>) in a <code>List</code> using the <code>+=</code> operator:</p> <pre><code>function : (children+=id '.')* last=id -&gt; ^($last) ; </code></pre> <p>and use a custom member-method in the parser to "inject" these <code>children</code> into the root of your tree (going from right to left in your <code>List</code>!):</p> <pre><code>function : (children+=id '.')* last=id {reverse($children, (CommonTree)$last.tree);} -&gt; ^($last) ; </code></pre> <p>A little demo:</p> <pre><code>grammar ReverseTree; options { output=AST; } tokens { ROOT; } @members { private void reverse(List nodes, CommonTree root) { if(nodes == null) return; for(int i = nodes.size()-1; i &gt;= 0; i--) { CommonTree temp = (CommonTree)nodes.get(i); root.addChild(temp); root = temp; } } } parse : function+ EOF -&gt; ^(ROOT function+) ; function : (children+=id '.')* last=id {reverse($children, (CommonTree)$last.tree);} -&gt; ^($last) ; id : ID ; ID : ('a'..'z' | 'A'..'Z')+ ; Space : ' ' {skip();} ; </code></pre> <p>And a little test class:</p> <pre><code>import org.antlr.runtime.*; import org.antlr.runtime.tree.*; import org.antlr.stringtemplate.*; public class Main { public static void main(String[] args) throws Exception { ANTLRStringStream in = new ANTLRStringStream("a.b.c.d.e Stack.Overflow.Horse singleNode"); ReverseTreeLexer lexer = new ReverseTreeLexer(in); CommonTokenStream tokens = new CommonTokenStream(lexer); ReverseTreeParser parser = new ReverseTreeParser(tokens); ReverseTreeParser.parse_return returnValue = parser.parse(); CommonTree tree = (CommonTree)returnValue.getTree(); DOTTreeGenerator gen = new DOTTreeGenerator(); StringTemplate st = gen.toDOT(tree); System.out.println(st); } } </code></pre> <p>which will produce an AST that looks like:</p> <p><img src="https://i.stack.imgur.com/ERNwr.png" alt="alt text"></p> <ul> <li>(image generated using <a href="http://graph.gafol.net" rel="nofollow noreferrer">http://graph.gafol.net</a>)</li> </ul> <p>For the input string:</p> <pre><code>"a.b.c.d.e Stack.Overflow.Horse singleNode" </code></pre>
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    1. CODamn - After hours of playing with my grammar I was hoping I was just missing a '^' in some place :(
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    2. CODo you have any suggestions of alternate routes I could explore? Different parser tools etc?
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    3. CO@Richie_W, check my EDIT.
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