  We establish a theory of NC functions on a class of von Neumann algebras with
a particular direct sum property, e.g. $B(\mathcal{H})$. In contrast to the
theory's origins, we do not rely on appealing to results from the matricial
case. We prove that the $k^{\text{th}}$ directional derivative of any NC
function at a scalar point is a $k$-linear homogeneous polynomial in its
directions. Consequences include the fact that NC functions defined on domains
containing scalar points can be uniformly approximated by free polynomials as
well as realization formulas for NC functions bounded on particular sets, e.g.
the non-commutative polydisk and non-commutative row ball.
