The Cubix framework for multi-language transformation. Explained in the OOPSLA 2018 paper "One Tool, Many Languages: Language-Parametric Transformation with Incremental Parametric Syntax"
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What is Cubix?

Cubix is a framework for language-parametric program transformation, i.e.: defining a single source-to-source program transformation tool that can be run on multiple languages. In Cubix, you can write transformations with a type signature like "This transformation works for any language that has assignments, loops, and a name-binding analysis," and instantly get separate tools for C, Java, etc. The goal is to radically reduce the cost of building sophisticated whole-program refactoring tools by allowing each tool to be built for a much larger market.

Cubix is based on the idea of incremental parametric syntax, a technique for defining families of representations of programming languages which share common components, and for defining them as a small modification to a pre-existing syntax definition. The name "Cubix" comes from the 2000s television show "Cubix: Robots for Everyone;" in that show, "Cubix" is a robot composed of modular pieces that can be reassembled for many purposes.

It currently supports C, Java, JavaScript, Lua, and Python.

The Cubix system itself, and the general incremental parametric syntax approach, is described in the OOPSLA 2018 paper:

  • One Tool, Many Languages: Language-Parametric Transformation with Incremental Parametric Syntax; James Koppel et al

We also recommend reading the following papers to get the necessary background in generic programming to understand Cubix:

  • Data Types à la Carte, Wouter Swierstra
  • Compositional Data Types, Patrick Bahr and Thomas Hvitved

Transformations in Cubix use our compstrat library of strategy combinators. To understand strategy combinators, we recommend the following paper:

  • The Essence of Strategic Programming, Ralf Lämmel et al

What Cubix is not

Cubix is the world's first framework that can build language-parametric source-to-source transformations. As the first of its kind, it often gets mistaken for a solution to more familiar problems. In particular, it is not:

  • A tool for translating one language into another. Cubix allows you to create a single tool that can transform C programs into better C programs and Java programs into better Java programs. It is not designed for building tools that can transform C programs into Java programs. Indeed, much of its power comes from its ability to preserve all the information of the original program.
  • A collection of ready-to-use refactoring tools. Thus far, all transformations built on Cubix are tech demos. While a couple are theoretically useful, they have not undergone the amount of UX engineering needed to actually be time-savers.
  • A framework for writing multi-language program analyses. Cubix transformations may consume results provided by other analyses, which may be written in either a single-language or multi-language fashion.
  • A framework for analysis/transformation of polyglot programs, i.e.: programs (or single source files) written in multiple languages.

However, Cubix's generic-programming capabilities make it a powerful tool for building all kinds of programming tools, even for only one language. We are particularly excited about the potential of extending Cubix to transform polyglot programs.

Getting started

To build Cubix:

First, download the sub-libraries comptrans and compstrat

git submodule update

Second, build Cubix:

stack build --ghc-options='-O0 -j +RTS -A256m -n2m -RTS'"

You may be prompted for your Github credentials to download the third-party frontends.

You are now ready to run Cubix transformations:

stack exec examples-multi java hoist input-files/java/

Compilation notes

Because of performance problems in GHC, the full Cubix will not build with -O1 or -O2. We've tried on a server with 64GB RAM; the server ran out of memory. Instead, use this command:

alias stackfastbuild="stack build --ghc-options='-O0 -j +RTS -A256m -n2m -RTS'"

This builds Cubix in parallel with minimal optimization, and sets the initial GHC heap to larger than usual.

We found the following two minimal sets of compilation flags that mitigate this blowup and make compilation manageable:

1: -fno-cse -fno-full-laziness 2: -fno-specialize -funfolding-creation-threshold=0

If disable everything except CSE and specialise, blow-up still occurs. Remains true with -O1

Adding "--flag cubix:only-one-language" to the build command will turn on a compile flag that disables building support for all languages except Lua, the smallest language. This greatly speeds compilation times, to the point where we are able to compile with -O2. Some of the performance reports in cubix/benchmarks/reports were compiled with this flag.

Directory Overview

Overview of directories (corresponding to the top-level of the zip file, and the /cubix directory on the Docker image): /stack.yaml # High-level build description /package.yaml # Low-level build description /examples # Example transformations built with Cubix /examples/multi # The main driver for the multi-language transformations /comptrans # Source code for the comptrans library /compstrat # Source code for compstrat, our library for Strategic Programming with Compositional Datatypes /input-files # Small test inputs in each of the 5 languages /scripts # Scripts for running the transformations over compiler test suites

Running the built-in transformations and analyses

Use this command from the "languages" directory (the one that contains "stack.yaml"):

stack exec examples-multi

You will be give the following help:

examples-multi <language> <transform> <file>*
examples-multi <language> <analysis>  <file>*
Transforms available: debug,id,cfg,elementary-hoist,hoist,tac,testcov,ipt
Analyses available: anal-triv-call

Note that only the IPT transformation can be run on multiple files.

For example, to run the three-address code transformation on a JavaScript file named "Foo.js", run: stack exec examples-multi javascript tac Foo.js

It can be faster to run the executable directory, without using stack exec. On the first author's laptop, this executable is located at .stack-work/dist/x86_64-osx/Cabal-

Using the Interprocedural Plumbing Transformation (IPT) Tool

We recommend also using the rlwrap command to enable command history.


rlwrap stack exec examples-multi java ipt input-files/java/ipt/*.java

In C and Java, you will additionally be prompted for the type of the parameter to add. Give this type as an AST for language-c or language-java (e.g.: (PrimType IntT), not int).

Running the language test suites

Cubix comes with scripts for running any semantics-preserving transformation on language test suites for C, Java, JavaScript, Lua, and Python, in the files scripts/test_java.rb and similar. To do so:

  1. Follow the below instructions to install the language tests.
  2. Each .rb file contains a constant at the top like JAVA_DIR and JAVA_TESTS pointing to the language implementation and tests directory. Modify these appropriately.
  3. Run ./scripts/test_<lang>.rb <name of transformation>

These scripts will run the transformation on all tests, run the transformed tests, and report the final pass/fail counts.

For all transformations except id, they will first run the identity transformation, and discard any tests that fail. This rules out tests that trigger bugs in the 3rd party parsers/pretty-printers, most (but not all) self-referential tests, and tests that the original language implementation fails.

They also come with a special count_loc parameter that counts the total lines of code in all relevant tests.

Installing GCC and GCC torture

Note: The C instructions are still being updated.

In some directory:

git clone
cd gcc

# If you want the same revision of gcc-torture as in the paper
git reset --hard f72de674726c5d054b9d99b0a4db09dfb52bf494

cd ..
mkdir gcc_build
cd gcc_build
make -j8
make install

Installing the K-Java test suite

In some directory:

git clone

# If you want the same revision as in the paper
cd java-semantics
git reset --hard c202266304340a2a4be81fa21ee4fe36b3117ee3

Installing test262, the JavaScript spec conformance tests, and the KJS test driver

In some directory:

git clone
cd javascript-semantics
git reset --hard d5aca308d12d3838c645e1f787e2abc9257ce43e # Only if you want the same revision as in the paper
make test262

The Lua tests

As described in the paper, we had to make several modifications to the Lua test suite to get them to run with Cubix. In particular, we removed several overly self-referential tests, and modified the test suite to report the number of passing/total assertions, rather than aborting the entire suite on the first failure.

These tests are in the test/lua/lua-5.3.3-tests directory.

Installing the CPython tests

In some directory:

git clone
cd cpython
git reset --hard 7bd4afec86849a57b48f375a9c4e0c32f0539dad # Only if you want the same revision as in the paper