Java Generics are Turing Complete

Radu Grigore

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arXiv · 1605.05274

Java Generics are Turing Complete

Radu Grigore

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Abstract

This paper describes a reduction from the halting problem of Turing machines to subtype checking in Java. It follows that subtype checking in Java is undecidable, which answers a question posed by Kennedy and Pierce in 2007. It also follows that Java's type checker can recognize any recursive language, which improves a result of Gil and Levy from 2016. The latter point is illustrated by a parser generator for fluent interfaces.

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Radu Grigore. 2016-11-07. Java Generics are Turing Complete. https://arxiv.org/abs/1605.05274

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