To simplify this even more you don't need to use the macro syntax in the transformation, simply use
<%# EvalText("DocumentName") %>
to get the rendered document name. If you want to get the current document name then simply use
<%# CMSContext.CurrentDocument.DocumentName %>
The difference between the two is CurrentDocument.DocumentName will be the document you are navigating to whereas the EvalText("DocumentName") will get the name of the document being rendered by the repeater from your dataset.