Arc/anarki is more minimalist than common lisp and won't warn you about unused variables, so I think the answer here is: nothing :) Here's the equivalent macro in anarki:
(mac tree-leaves (tree test result)
`(tree-leaves%% ,tree ,test ,result))
Might as well call the function directly :)
(And no, this wasn't asked before. I'd never gotten past the first couple of chapters of letoverlambda. Maybe I should go back to it.)
Hey thanks for saving me further embarrassment. If I were to ask another question should I start another thread? In particular I am trying to translate to arc a matching function in Paul Graham's On Lisp, Fig 18.5. After this I am hoping to learn about Query Interpreters Fig 19.3 and Query Compilers Fig 19.6