GPCE Demonstration 23

Implementation of DSLs using staged interpreters in MetaOCaml

Kedar Swadi, Rice University

Summary

Domain-specific languages (DSLs) allow programmers to write applications faster than in general-purpose languages. Two approaches are commonly taken to implement DSLs. The first is to compile the DSLs into machine-level code, or low-level languages such as C. While this results in fast implementations, writing compilers requires expertise in compiler technology, and long implementation times. An alternative approach uses interpreters to implement DSLs. Though easier to write, extend and maintain than compilers, the overhead of interpretation is unacceptably large for many applications. Relevance to GPCE and uniqueness of approach: The shortcomings in either approaches significantly impede the widespread use of DSL-based generative programming in software development. The demonstration addresses this problem using multistage programming. It shows how staged interpreters for implementing DSLs avoid problems in both abovementioned approaches, and allow efficient machine-level realizations of DSL programs. Unlike other existing approaches, this approach guarantees that the generated code is typesafe. Underlying implementation techniques and technologies used: This demonstration uses multistage programming in the MetaOCaml language to write two-stage interpreters which translate DSL programs into OCaml programs, which are finally compiled into efficient machine code and executed.

First a quick introduction to multistage programming is given using a simple example of the power function that computes x^n. The demonstration shows how three staging constructs in MetaOCaml are used to automatically generate typesafe specialised versions of this function from the generic function.

Second, the demonstration shows how to implement a staged interpreter for a small language and how to correctly measure performance of implementations. Finally, the demonstration visually shows performance gains from a staged interpreter for the LOGO graphics language. This is done by concurrently running the graphical outputs for the simple and staged interpreters on two windows placed side-by-side.

Research papers and information about downloading, installing, and using MetaOCaml are found at http://www.metaocaml.org.

Times and Locations

• Tue, 26 Oct., 15.30 - 16.15, Exhibition Hall Demo Room 4
• Thu, 28 Oct., 12.30 - 13.15, Exhibition Hall Demo Room 4