Professor Tom Reps retires after 39 years of research and mentorship

By Rachel Robey

As he retires, Professor Tom Reps will endow a professorship named in honor of his late wife (and CS Professor Emerita) Susan Beth Horwitz.

It is with tremendous gratitude that the Department of Computer Sciences (CS) announces the retirement of Professor Thomas W. Reps, the J. Barkley Rosser Professor and Rajiv and Ritu Batra Chair of Computer Sciences. After 39 fruitful years, he will be sorely missed on campus — and especially in the hallways of tower three, floor six (home to madPL, UW–Madison’s Programming Languages group). It is a consolation that we can also look forward to welcoming him back as professor emeritus. 

In addition to Reps’ numerous research contributions and services to CS, many of which are detailed below, we have yet another reason to be grateful. As he departs, he is endowing a new professorship in honor of his late wife Susan Beth Horwitz, who was also a UW–Madison CS professor from 1985 until her passing ten years ago. Like Reps, Horwitz spent her career supporting and uplifting the excellence of CS and madPL. 

Honoring the careers of Tom Reps and Susan Horwitz 

Tom Reps and Susan Horwitz skiing on vacation in the Jura Mountains in 2007.

UW–Madison is a no-brainer for young researchers and early career faculty, as Reps and Horwitz quickly discovered when they entered the academic market in 1985. Reps (a sailor-turned-computer scientist) and Horwitz (an avid equestrian, outdoorsperson, painter, quilter, and pianist, among numerous other creative pursuits) were told in no uncertain terms by Reps’s mother that Madison, where she had been a graduate student in 1944, was the exact right place for them.

“The word I got from both my parents  was, ‘Don’t get your heart set on any place until you’ve seen Madison,’” says Reps. “Well, they were right.” In addition to enjoying Madison’s outdoor activities and excellent food scene, Reps and Horwitz found a welcome home in CS. As the second and third programming-languages specialists hired by the department, they worked with (then-Chair) Charles Fischer to grow the now flourishing madPL group from the ground up.  

A quote from G. Ramalingam PhD’93 says, “Tom is an outstanding researcher and educator. His research work is always elegant, built with a strong theoretical foundation, with a long-lasting value. A hallmark of his papers and writing is great clarity in thought and communication.”

Throughout their tenures, each went on to have a highly impactful career. Reps focused on research, authoring four books and well over 200 academic papers, for which he has won numerous awards. With Horwitz, he co-led the Wisconsin Program-Slicing Project research group and wrote (along with co-author/former student David Binkley PhD’91) one of the 50 most influential papers according to the ACM SIGPLAN Conference on Programming Language Design and Implementation. Alongside tens of thousands of citations, Reps has also earned dozens of awards, including the NSF Presidential Young Investigator Award (1986), a Packard Fellowship (1988), a Humboldt Research Award (2000), a Guggenheim Fellowship (2000), the  ACM SIGPLAN Programming Languages Achievement Award (2017), and recently the CAV Award (2023).  

A quote attributed to Komondoor V. Raghavan PhD’03 says, “Susan was the hallmark of dedication and rigor in research. Her immense creativity is also evidenced by her stellar record of high-impact ideas and inventions that are used to this day by researchers and tool designers. She continues to guide my work.”

In an article published in Times Higher Education, Horwitz was noted as “an expert in software-development environments, dataflow, and pointer analysis,” who, at the time of her passing, was “ranked 37th for programming languages (out of 50,000 published authors in the field).” Active in the scientific community, Reps estimates she sat on the NSF Graduate Fellowship Selection Committee “15 or 20 times” and the Advanced Placement Computer Science Test Development Committee for ten years, five of which she served as chair. Of her numerous scientific contributions, an algorithm adopted by Microsoft’s SLAM tool “to detect the bugs that were causing about 85 percent of the crashes in Windows” is considered by many to be her most widely impactful result.

A quote attributed to Tom Ball PhD’93 says, “I will remember Susan Horwitz for her wide-ranging interests and excellence in computing research. She was a superb pianist and very supportive of my desire to balance computer science with a music minor at Wisconsin. I will always be grateful for her mentorship.” Horwitz’ later career was motivated by a clear need to make an education in computer science more accessible. At UW-Madison, she organized and led Wisconsin Emerging Scholars-Computer Sciences (WES-CS) and Women in Science and Engineering (WISE), both dedicated to supporting women and underrepresented minorities pursuing STEM educations. 

Thanks in part to Reps’ and Horwitz’s hard work and innovative research, the department continues to flourish and is now ranked 11 in programming languages by U.S. News and World Report

Susan Beth Horwitz Professorship will ensure continued excellence

Horwitz leads a WES-CS lecture.

In the future, the Susan Beth Horwitz Professorship will help sustain the department’s track record of excellence. In a way, it will sustain Susan’s memory as well. “It’s  a way for me to make sure that she’s remembered in the department,” says Reps.  “And now seems like the right time to commemorate her in that way.” 

As for why he believes a professorship to be the best course? 

“We have fantastic people on the faculty, and a professorship is one of the ways that the university can recognize them,” he continues. “It was Remzi [Arpaci-Dusseau] who pointed out that, while we have plenty of professorships and chairs aimed at senior faculty, we don’t have much for mid-career people. Yet that’s who you don’t want to lose, because they’re at the prime of their career and charging along with research programs running on all cylinders.”

A quote attributed to Suan Yong PhD’04 says, “Susan was a great educator and would sometimes employ props to help students understand abstract ideas more effectively than just slides and bullet points. She was also a trusted PhD advisor, mentor, and research collaborator, and probably the most influential person in shaping the trajectory of my professional career.”

CS Chair Steve Wright agrees. “The new Susan Beth Horwitz Professorship will boost our efforts to support and retain energetic faculty members who are expanding and possibly reorienting their research programs in the years after tenure,” he says. “I can’t help thinking that Susan would have been delighted by this initiative and by Tom’s thoughtfulness and generosity.”

Tom’s parting gift seeks to ensure that research excellence is preserved in the department. By splitting its impact between the Susan Beth Horwitz Professorship and madPL, Reps will both support mid-career faculty and help UW-Madison remain a leader in programming languages. 

Toasting a cherished collaborator, colleague, and friend

A quote attributed to Gogul Balakrishnan PhD’07 syas, “At grad school and beyond, Tom has been a source of constant support and inspiration. He instilled in me the discipline to think from first principles, as well as the desire to seek practical applications of my research. Without an iota of exaggeration, most of what I am as a researcher is due to Tom."

“Besides being a ground-breaking researcher and a leader of the programming languages community, Tom has been an exemplary citizen of the CS department,” says CS Chair Steve Wright.  “In a recent meeting, our colleague Efty Sifakis called Tom ‘the soul of the department,’ an appellation that resonated strongly with all of us.” 

After an impressive career, Reps plans to model “retirement” after his father’s: “He just kept going to the office. When he was a professor of city planning history at Cornell, he wrote nine books. As emeritus professor, he wrote five more,” Reps says. “He would tell my mother, ‘I’m off for my bath in the fountain of youth.’” 

A quote attributed to Aditya Thakur PhD’14 says, “Tom's research stands out for its depth and breadth, and his foundational results are not only taught in university courses but widely deployed in industry tools. One of the most valuable lessons I learned from him was the ability to focus on the details without being fixated by them, thus, being able to pivot to more promising research directions.”

We look forward to welcoming Reps back as professor emeritus in fall 2024. Until then, though, he has several (“actually, a few too many”) collaborations to tide him over. “I have a big collaboration with Loris D’Antoni and a long-time collaboration with Zak Kincaid at Princeton,” says Reps, before listing collaborators at Leiden University, Peking University, CMU, UT-Austin, Georgia Tech, Stony Brook University, IIT-Kanpur, and Rice University.

For D’Antoni, also a member of madPL, the value of working and learning from Reps has been incalculable. “As a mentor, Tom made sure I would succeed: He provided invaluable feedback whenever I asked and supported my ideas and my work,” he says. “His encyclopedic knowledge of formal-methods results, his clear thinking, and his high standards for writing have taught me to always aim for the highest quality in research.”

A quote attributed to Somesh Jha, Lubar Professor of Computer Sciences, says, “When I joined the department in 2000, Tom Reps and I collaborated on several research projects and grants. He’s one of the deepest thinkers I have interacted with. He and his late wife Susan Horwitz had a profound impact on my research career.” A quote attributed to Nicholas Kidd PhD’09 says, “Tom was a great PhD advisor and an even better friend. The impact he had on his students was evident when nearly all of his 24 PhD graduates and many more colleagues attended his “Last Lecture.” Tom's exemplary career sets the bar that new professors aspire to achieve.”

So, on behalf of the department in its entirety: Thank you, Tom, for your and Susan’s years of dedication to the department, the field of computer science, and your Madison community. We look forward to seeing you in the new building in your new role as emeritus professor and to the bright future of CS and madPL.