Title: The Spoofax Propositional Language

Stratego Transformations in the Spoofax Eclipse IDE

The Stratego Tutorial/Reference {! docrefs/manual.md !} in the official Spoofax documentation presents a comprehensive overview of the Stratego approach to abstract syntax tree (AST) transformations. It employs a running example of an abstract syntax intended to represent classical Propositional Logic, which we will dub here the "Spoofax Propositional Language." The manual introduces the concepts of rules and strategies for applying them, and then shows how both of those facilities can be created from more primitive operations of term matching and replacement. Every step of the way is illustrated with actual, working Stratego programs.

There are, however, two catches for a newcomer trying to learn Spoofax and Stratego for the first time:

1. All of the examples are worked in an older framework ("Stratego/XT") which has a rather different collection of tools than the current implementation of Spoofax in the Eclipse IDE.
2. Unlike with the Calc example language used for the explication of the Syntax Definition Language SDF3, there does not seem to be any publicly available repository containing the worked examples to follow along with.

This Gitea repository aims to fill both gaps. It can be cloned as an Eclipse project (note the git root is at the project level rather than in the directory above the project, as may be more common; in other words, this repository should be cloned within an existing Eclipse workspace, rather than as the workspace itself). Within that project, (ultimately) every example from the Stratego Tutorial manual starting from Section 4 on can be executed directly. And this (Mkdocs-generated) documentation seeks to clarify the ways that Stratego transformations may be run in the Spoofax/Eclipse IDE environment, serving as a supplement/replacement for the portions of the manual that were specific to Stratego/XT.

Preliminaries

I recommend working with a complete pre-built Eclipse installation of Spoofax as provided by the Spoofax project, for example one that you can download from their development release page. I have been unable to get the examples in this repository working starting from plain Eclipse and installing Spoofax in it using the Spoofax update site.

If at any point in using the examples things appear to stop working, and especially if the Spoofax menu item disappears or the Spoofax menu turns into a thin white rectangle with no items to select, try the following:

• Build the project and try again.
• Clean the workspace, and when it is done, build the project again and try again.
• Right click on the project, select Maven > Update Project, make sure everything is checked except "Offline" and "Force update of Snapshots/Releases", and then click "OK". When it is done, clean the workspace, then build the project and try again.
• If that still hasn't done it, restart (the Spoofax version of!) Eclipse and clean the workspace, then build the project and try again.

Running with a version of Spoofax later than 2.5.13 (I was using a 2.6.0 development snapshot), the Spoofax menu would always come back into proper operation at some point in the above process.

Abstract syntax

With the preliminaries out of the way, let's begin delving into Stratego transformations by recalling the abstract syntax of the Spoofax Propositional Language (SPL), as defined at the top of {! docrefs/sec4.1.md !} of the manual. It consists of the following signature of constructors:

{! src-gen/signatures/Spoofax-Propositional-Language-sig.str extract:
  start: '(signature[\s]*)$'
  stop: '^(\s*Eq\s*:.*)'
!}

Continue reading in the latest released SPL documentation to see how to define and run Stratego transformations on ASTs of this language.