  We introduce the notion of feedback computable functions from $2^\omega$ to
$2^\omega$, extending feedback Turing computation in analogy with the standard
notion of computability for functions from $2^\omega$ to $2^\omega$. We then
show that the feedback computable functions are precisely the effectively Borel
functions. With this as motivation we define the notion of a feedback
computable function on a structure, independent of any coding of the structure
as a real. We show that this notion is absolute, and as an example characterize
those functions that are computable from a Gandy ordinal with some finite
subset distinguished.
