Well, this would indeed be a very useful extension - I've actually seen many use cases, where new users ran into issues with simple expressions like X[i,i] = foo(). In the general case, the problem with UDFs is that they can have - in contrast to builtin functions - multiple returns. These multiple returns would translate to HOPs with multiple outputs, which in turn cannot be represented with our current HOP DAG representation because a HOP represents an operation and the characteristics of a single output, but potentially with many consumers. This is also the reason why builtin functions with multiple outputs (i.e., lu, eigen, qr) are internally mapped to FunctionOps with the same restrictions.
However, we could actually allow UDFs with a single output in expressions. This would require a generalization of how results variables are bound but should not take too much effort. Additional it would require a full pass through the compiler to remove any assumptions that FunctionOps always appear as DAG root nodes. Bottom line: We could realistically add it to our feature list for the 1.0 release. Regards, Matthias On Wed, Mar 29, 2017 at 3:55 PM, <dusenberr...@gmail.com> wrote: > Currently, it is not possible to use UDFs within an expression. I.e. I'd > like to be able to use something like `out = (-1/2) * > util::my_function(x)`. This would of course extend to more elaborate > expressions. Also, note that we *are* able to use built-in functions > within expressions. > > I think it would be good to allow for this. Are there any issues that > would make this difficult? > > -Mike > > -- > > Mike Dusenberry > GitHub: github.com/dusenberrymw > LinkedIn: linkedin.com/in/mikedusenberry > > Sent from my iPhone. > >
