Trees that Grow in the Paragon Compiler A Step Towards Modularity

Abstract: Paragon is a programming language that extends Java with statically checked information flow control policies. Paragon’s compiler, which is written in Haskell, has a large type checker. Its current implementation is monolithic, making the compiler challenging to develop. Paragon’s authors, Broberg et al., have proposed to partition the type checker into five phases, and this project is a step towards such an implementation. We identify the representation of Paragon’s abstract syntax tree as an essential design aspect and emphasize extensibility to conform to the phases’ varying requirements. Based on a programming idiom, Trees that Grow, by Najd and Jones, we implement an extensible abstract syntax tree in Paragon’s compiler. We observe that our implementation introduces a substantial amount of boilerplate code. To alleviate the issue, we employ several methods for generic programming. We conclude that our AST implementation is extensible but complex.