Sound type-dependent syntactic language extension

8 years 18 days ago

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Syntactic language extensions can introduce new facilities into a programming language while requiring little implementation eﬀort and modest changes to the compiler. It is typical to desugar language extensions in a distinguished compiler phase after parsing or type checking, not aﬀecting any of the later compiler phases. If desugaring happens before type checking, the desugaring cannot depend on typing information and type errors are reported in terms of the generated code. If desugaring happens after type checking, the code generated by the desugaring is not type checked and may introduce vulnerabilities. Both options are undesirable. We propose a system for syntactic extensibility where desugaring happens after type checking and desugarings are guaranteed to only generate well-typed code. A major novelty of our work is that desugarings operate on typing derivations instead of plain syntax trees. This provides desugarings access to typing information and forms the basis for the...

Florian Lorenzen, Sebastian Erdweg

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