Rough Draft of xdc While Lowering

const lowerWhileStatement =
{
    // Apologies in advance if this isn't actually valid D code:
    //   This is a design sketch and I currently don't have a way to compile it.
    //
    // The Pattern template, PatternMatch template, and PatternHandler class
    //   have not yet been written.  This is an example of how I might expect
    //   them to be used.
    //

    auto consumes = "while_statement";
    auto produces = "if_statement","goto","label");

    auto recognizer = Pattern!
        "WhileStatement has
        {
            // Capture the conditional expression (call it "expr") and
            //   capture the loop body (call it "statement").
            .expression $expr;
            .statement  $statement has
            {
                // Capture any continue/break statements.
                any_amount_of {
                    any_amount_of .; // Same as .* in regexes.
                    one_of
                    {
                        ContinueStatement $continues;
                        BreakStatement    $breaks;
                    }
                }
                any_amount_of .;
            }
        }";

    auto action = (PatternMatch!(recognizer) m)
    {
        m.captures.add("uniqLoopAgain", getUniqueLabel(syntaxNode.enclosingScope))
        m.captures.add("uniqExitLoop", getUniqueLabel(syntaxNode.enclosingScope))

        // The "recognizes" clause defines m.getCapture!"continues" with:
        //   "ContinueStatement $continues;"
        // That line appears in a repitition context ("any_amount_of") and is
        //   therefore typed as an array.
        foreach( ref node; m.getCapture!"continues" )
            node.replaceWith( m, "GotoStatement has $uniqLoopAgain" )

        // Ditto for m.getCapture!"breaks" and "BreakStatement $breaks;".
        foreach( ref node; m.getCapture!"breaks" )
            node.replaceWith( m, "GotoStatement has $uniqExitLoop" )
    };

    auto synthesizer = Pattern!
        "Label has $uniqLoopAgain
        IfStatement has
        {
            OpNegate has $expr
            GotoStatement has $uniqExitLoop
        }
        $statement
        GotoStatement has $uniqLoopAgain
        Label has $uniqExitLoop
        ";

    return new PatternHandler(produces, consumes, recognizer, action, synthesizer);
};