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This book constitutes the refereed proceedings of the 12th Asian Symposium on Programming Languages and Systems, APLAS 2014, held in Singapore, Singapore in November 2014. The 20 regular papers presented together with the abstracts of 3 invited talks were carefully reviewed and selected from 57 submissions. The papers cover a variety of foundational and practical issues in programming languages and systems - ranging from foundational to practical issues. The papers focus on topics such as semantics, logics, foundational theory; design of languages, type systems and foundational calculi; domain-specific languages; compilers, interpreters, abstract machines; program derivation, synthesis and transformation; program analysis, verification, model-checking; logic, constraint, probabilistic and quantum programming; software security; concurrency and parallelism; as well as tools and environments for programming and implementation.

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NetKAT - A Formal System for the Verification of Networks.- Optimized Compilation of Multiset Rewriting with Comprehensions.- Logic Programming and Logarithmic Space.- Automatic Memory Management Based on Program Transformation Using Ownership.- The Essence of Ruby.- Types for Flexible Objects.- A Translation of Intersection and Union Types for the mi -Calculus.- A Formalized Proof of Strong Normalization for Guarded Recursive Types.- Functional Pearl: Nearest Shelters in Manhattan.- Suppl: A Flexible Language for Policies.- A Method for Scalable and Precise Bug Finding Using Program Analysis and Model Checking.- Model-Checking for Android Malware Detection.- Necessary and Sufficient Preconditions via Eager Abstraction.- Resource Protection Using Atomics: Patterns and Verification.- Resource Analysis of Complex Programs with Cost Equations.- Simple and Efficient Algorithms for Octagons.- Compositional Entailment Checking for a Fragment of Separation Logic.- Automatic Constrained Rewriting Induction towards Verifying Procedural Programs.- A ZDD-Based Efficient Higher-Order Model Checking Algorithm.- Inferring Grammatical Summaries of String Values.- Syntax-Directed Divide-and-Conquer Data-Flow Analysis.- Address Chain: Profiling Java Objects without Overhead in Java Heaps.- Call-by-Value in a Basic Logic for Interaction.- A Precise and Abstract Memory Model for C Using Symbolic Values.- Hereditary History-Preserving Bisimilarity: Logics and Automata.

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