Abstract

Multi-stage programming (MSP) provides a safe way of generating code at run-time. In mostly-functional languages like MetaOCaml, this has been used to reduce the performance penalties of abstractions such as loops, recursion or interpretation. The main advantage of MSP compared to other techniques, such as string or LISP quotations, is that MSP guarantees type safety for the generated code statically, at the time the program is compiled.

Unfortunately, MSP is difficult to combine with imperative features found in most mainstream languages like Java. The central problem is “scope extrusion”, which may accidentally move variables outside the scopes in which they are bound, leading to run-time errors in the generated code. This problem can be prevented if code in escapes (or “anti-quotes”) is “weakly separable”, i.e. the computational effects occurring inside an escape that are visible from the outside do not involve code.

We have formalized a type system, based on Lightweight Java, that uses weak separability to prevent scope extrusion, and we have proved that the type system is sound. We have also developed an implementation called Mint to demonstrate the expressivity of the type system and the performance benefits MSP can provide in an imperative setting. Since our implementation extends the Java language, our work is accessible to mainstream programmers.

This talk is based on work will be presented at the Conference on Programming Language Design and Implementation (PLDI 2010). More information is available at http://mint.concutest.org/