Stephen Mell

sm1@cis.upenn.edu | GitHub | Google Scholar | DLBP | OrcID

Computer science PhD student at the University of Pennsylvania, advised by Osbert Bastani and Steve Zdancewic and member of the Programming Languages Club and the ASSET Center for Safe, Explainable, and Trustworthy AI.

Research

Preprints

• Opportunistically Parallel Lambda Calculus. Or, Lambda: The Ultimate LLM Scripting Language
  In Preparation. Stephen Mell, Konstantinos Kallas, Steve Zdancewic, Osbert Bastani
  arXiv
• A Scripting Carol: How (Not) to Optimize Scripts that Glue
  In Submission. Stephen Mell, Osbert Bastani, Steve Zdancewic, Konstantinos Kallas

Conference Publications

• Optimal Program Synthesis via Abstract Interpretation
  POPL 2024. Stephen Mell, Steve Zdancewic, Osbert Bastani
  Pub | arXiv | Artifact | Talk | Slides
• Synthesizing Trajectory Queries from Examples
  CAV 2023. Stephen Mell, Favyen Bastani, Steve Zdancewic, Osbert Bastani
  Pub | Extended/arXiv | Artifact | Talk | Slides
• PAC Prediction Sets for Large Language Models of Code
  ICML 2023. Adam Khakhar, Stephen Mell, Osbert Bastani
  Pub | arXiv
• Counterfactual Explanations for Natural Language Interfaces
  ACL 2022. George Tolkachev, Stephen Mell, Stephan Zdancewic, Osbert Bastani
  Pub | arXiv

Other Publications

• Ideograph: A Language for Expressing and Manipulating Structured Data
  TERMGRAPH 2022. Stephen Mell, Osbert Bastani, Steve Zdancewic
  Pub | Talk | Slides
• Synthesizing Video Trajectory Queries
  AIPLANS (NeurIPS 2021 workshop).
  Stephen Mell, Favyen Bastani, Stephan Zdancewic, Osbert Bastani
  Pub
• Securing Election Infrastructure with Hand-Marked Paper Ballots
  JSPG 2020. Varun Gupta, Joel Hypolite, Stephen Mell, Hersh Sanghvi^†
  Pub
• Safe Predictors for Enforcing Input-Output Specifications
  NeurIPS 2019 workshops. Stephen Mell, Olivia Brown, Justin Goodwin, Sung-Hyun Son
  Pub

† Ordered alphabetically

Invited Talks

• UW PLSE, 2025. Opportunistic Lambda Calculus: Automatic Parallelization and Streaming for Scripting
• NJPLS, 2024. Opportunistic Lambda Calculus: Automatic Parallelization and Streaming for Scripting
• UT Austin UToPiA, 2024. Opportunistically Parallel Lambda Calculus. Or, Lambda: The Ultimate LLM Scripting Language

Funding

• Amazon/ASSET Gift for Research in Trustworthy AI, 2023

Teaching

• CIS191: Linux/Unix Skills. University of Pennsylvania, Spring 2021
  Course Designer and Instructor

Service

• Student Volunteer Co-Chair. POPL 2025
• Mentor, Reading Group Facilitator. REPL REU 2024
• Mentor. REPL REU 2023
• External Reviewer. ESOP 2024
• Reviewer. AIPLANS 2021 (Workshop)
• Office Committee. CIS Department 2022, 2023

Education

• PhD in Computer Science. University of Pennsylvania, Fall 2019 - Present
• BA in Mathematics. Washington University in St. Louis, Fall 2014 - Spring 2019
  GPA: 3.96/4.00, Phi Beta Kappa

Emplyment

• Summer Research Associate. Topos Institute, Summer 2023
• Research Intern. MIT Lincoln Lab, Summer 2019
• REU in Software Engineering. Carnegie Mellon University, Summer 2018
• Software Developer. Mellware, 2016 - 2019
• Software Developer. Finsight LLC, 2013 - 2016