<joly> (doc binding)
<sexpbot> ⟹ "Macro ([bindings & body]); binding => var-symbol
init-expr Creates new bindings for the (already-existing) vars, with
the supplied initial values, executes the exprs in an implicit do,
then re-establishes the bindings that existed before. The new bindings
are made in parallel (unlike let); all init-exprs are evaluated before
the vars are bound to their new values."