Programming languages and systems : 19th Asian symposium APLAS 2021 Chicago IL USA October 17 18 2021 : proceedings Analysis and Synthesis Scalable and Modular Robustness Analysis of Deep Neural Networks Function Pointer Eliminator for C Programs PyCT: A Python Concolic Tester Program Synthesis for Musicians: A Usability Testbed for Temporal Logic Specifications Server Side Computation of Package Dependencies in Package Management Systems Compilation and Transformation Fully Abstract and Robust Compilation and How to Reconcile the Two Abstractly A Dictionary Passing Translation of Featherweight Go Hybrid quantum classical circuit simplification with the ZX calculus A compilation method for dynamic typing in ML Language Design The Choice Construct in the Souffle Language Latent Effects for Reusable Language Components Adaptable Traces for Program Explanations A Typed Programmatic Interface to Contracts on the Blockchain Verification Simplifying of Alternating Automata for Emptiness Testing Termination Analysis for the pi Calculus by Reduction to Sequential Program Termination Proving LTL Properties of Bitvector Programs and Decompiled Binaries Solving Not Substring Constraint with Flat Abstraction. . This book constitutes the proceedings of the 19th Asian Symposium on Programming Languages and Systems APLAS 2021 held in Chicago USA in October 2021.* The 17 papers presented in this volume were carefully reviewed and selected from 43 submissions. They were organized in topical sections named: analysis and synthesis compilation and transformation language and verification. * The conference was held in a hybrid format due to the COVID 19 pandemic