Stephen Wolfram wrote the following tribute to Robby.
With the tragic death of Robby Villegas, the world has lost an exceptional mind, and one of the great scholars and guardians of the Mathematica language. It was June 6, 1992, on a pleasant sunny day, just after an honorary degree ceremony at Knox College in Galesberg, Illinois. An eager young man who had just received his own degree came up to me, keen to tell me that he thought that the design of the function
Outer in Mathematica was inadequate, and needed to be enhanced. We talked for quite a while. And eventually I said, “So what are you doing now that you’ve graduated? We’re hiring people at our company to work on Mathematica; you should come and join us.” And so it was that on June 29, 1992, Robby Villegas came to join Wolfram Research.
In the 15 years that followed, my email archive records more than 10,000 messages that include his name, with the number peaking in 1995. The syntax and semantics of a zillion functions. Ideas for extending, generalizing, clarifying features in Mathematica. A vast amount of work concerned with getting things in Mathematica just right. In making everything as clean and logical as it could be. In many ways, Robby Villegas was the first full-time design analyst for Mathematica. I think he personally knew every function in the system—its character, and its quirks.
And pretty soon when people were discussing some abstruse (or not so abstruse) potential feature of some new Mathematica function, I would just say, “Ask Robby; he’ll be able to figure it out.”
Robby Villegas contributed a great many ideas to Mathematica. To list manipulation and functional programming operations. And to mathematical typesetting, and the MathML web standard.
We have been lucky enough with Mathematica to be able to build a very pure and robust intellectual structure, that we can progressively add to over the years. Robby Villegas was the architect of some of the most demanding and elegant sections of this structure.
I remember one day when we were discussing some function or another, and someone was saying that we should do something in a particular way, because that’s how some other function in Mathematica worked. And Robby Villegas said that perhaps that precedent was not so good, because that other function was designed very early in the history of Mathematica, when designs were rougher.
And in that moment I realized that Robby Villegas had become the first true scholar of the Mathematica language. With an understanding not only of its current structure, but also the whole arc of its history. With his eagerness, he seemed in many ways so young. But yet he brought to his judgment about Mathematica a certain seasoned wisdom.
Over the years, I worked on many projects with Robby Villegas. From all sorts of detailed pieces of Mathematica design, to the emergency need to produce Mathematica code for notation for numbers and polynomials from antiquity (code that lives on for example in Wolfram|Alpha).
In later years, there were times when it could take a while to hear from Robby Villegas. But always the responses were careful, clear, and creative. And profoundly committed to making sure that the Mathematica language that we have all created remained as elegant and unified as possible.
There are countless specific functions in Mathematica that owe their structure and syntax to Robby Villegas. And as the system grows, these functions become the cornerstones of yet more development—building on the legacy of Robby Villegas.
Every day, around the world, people use those functions that Robby Villegas designed. And though all will benefit from it, few will pause to admire the elegance of the design. Or know about the wonderful human being who put so much effort into creating and ensuring that elegance: Robby Villegas, a great scholar and guardian of the Mathematica language, and its first true design analyst.