  Users often rely on GUIs to edit and interact with visualizations - a
daunting task due to the large space of editing options. As a result, users are
either overwhelmed by a complex UI or constrained by a custom UI with a
tailored, fixed subset of options with limited editing flexibility. Natural
Language Interfaces (NLIs) are emerging as a feasible alternative for users to
specify edits. However, NLIs forgo the advantages of traditional GUI: the
ability to explore and repeat edits and see instant visual feedback.
  We introduce DynaVis, which blends natural language and dynamically
synthesized UI widgets. As the user describes an editing task in natural
language, DynaVis performs the edit and synthesizes a persistent widget that
the user can interact with to make further modifications. Study participants
(n=24) preferred DynaVis over the NLI-only interface citing ease of further
edits and editing confidence due to immediate visual feedback.
