Strategic Language Workbench Improvements

Jeff Smits

Computers execute software to do the tasks we expect from them. This software is written by human beings, we call this programming. The most common way to program is by writing text in a programming language. A programming language is very structured so we can be precise, but ultimately these languages are still for humans to read and write. In order to execute the written program, we need to translate it to a list of tiny instruction steps that the hardware of the computer can execute. This translation is also automated with software. The most common forms this software takes is (1) interpreters that execute a program live as they read it, or (2) compilers that translate the entire program for later execution.

Interpreters and compilers are tools of the domain of Programming Languages (PL). Apart from interpreters and compilers, there is more support software available around programming languages. This includes smart text editors, program analysis, running-program observers, etc. The requirements for PL tools are high: they should not get in the way when used to create software. In particular, they should support useful features, be fast enough in interaction, and not make mistakes.

Given these requirements, it is not a simple task to make PL tools. In an effort to make it easier to create PL tools, Language Workbenches (LWBs) were created: a suite of tools specifically for creating PL tools.

In this dissertation, you can find several improvements I made to a particular language workbench. I have—in multiple ways—sped up the language development cycle in this workbench: in terms of improved development, feedback, and execution speed.

Throughout my research, I have worked on and in the Spoofax language workbench, a research language workbench used for programming language research at TU Delft. Spoofax splits up the specification of programming languages into different domains, and captures each of those domains in a meta-language. For example, to describe the structure of the text of a programming language, Spoofax uses a formalism based on context-free grammars, extended with different useful features, which is called the Syntax Definition Formalism 3 or SDF3 for short. Similarly, there are meta-languages for the description of names, references and types; for what it means to execute a program; for defining assumptions and behaviour by example for testing purposes; and for transforming programs, which is a catch-all, but still a fairly high-level language. This language for transforming programs, called Stratego, is particularly relevant to this dissertation.

Contributions. Firstly, we introduce a new meta-language specialised in control- and data-flow analysis: FlowSpec. FlowSpec improves the development speed of programming languages in Spoofax, and the feedback in Spoofax and in the PL tools generated by Spoofax.Secondly, we improve the compilation speed of Stratego on successive compilations with an incremental compiler. This compiler improves the speed at which you receive feedback inside Spoofax on changes to a Stratego program, and the speed at which you can see the results of tests and other short program executions after a change.

Thirdly, we add a gradual type system to Stratego to improve the feedback that can be given without executing Stratego programs. A gradual type system does not require a user of Stratego to add types to their program, but if they choose to, the gradual type system will be able to reason about the parts of the program that are typed, and give certain errors at compilation time instead of run time.

Finally, we develop a pattern matching optimisation that work for Stratego’s pattern matching. This improves the execution speed of Stratego programs. Since all PL tools created in Spoofax include at least some of those Stratego programs, this also speeds up the execution of the Spoofax meta-languages themselves.

Reference

Jeff Smits. Strategic Language Workbench Improvements. PhD thesis, TU Delft. September 2023.

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