paterl - Erlang to Pat transpiler

The current type-checking pipeline consists of these stages:

1. epp:parse_file: Erlang preprocessor (parsing and macro expansion)
2. paterl_syntax:module: Rule out unsupported Erlang syntactic subset (not implemented)
3. erl_lint:module: Erlang linting
4. paterl_ir:module: Assignment transformation which expands Erlang expressions to match (will implement ANF next)
5. paterl_types:table: Extract Erlang typespec annotations into a table
6. paterl_bootstrap:forms: Modifies the Erlang syntax tree to insert an auxiliary bootstrapping main function
7. paterl_anno:annotate: Annotates the Erlang syntax tree using the type information in the table obtained from step 5
8. paterl_trans:module: Translates the annotated Erlang syntax tree to a Pat syntax tree
9. pat_prettypr:module: Prints the Pat syntax tree

Using from the Erlang shell

paterl:compile("src/examples/erlang/codebeam/id_server_demo.erl", [{includes, ["include"]}, {out, "out"}]).

Using from the terminal

./src/paterl src/examples/erlang/codebeam/id_server_demo.erl -v all -I include

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Installing the paterl toolchain

The following instructions detail how paterl can be installed on MacOS, Ubuntu, and Windows.

Install the Windows Subsystem for Linux

The simplest and ideal way to install paterl on Windows is to use the Windows Subsystem for Linux (WSL). WSL provides virtualised Linux environment on Hyper-V. While WSL can access your Windows file system, software installed on the virtualised Linux environment is isolated from and cannot be accessed by Windows, and vice versa. This means that packages (e.g. Erlang) installed on Windows must also be installed in the virtualised Linux environment to be available to Linux.

1. By default, WSL installs the latest Ubuntu distribution. This is done by typing the following on your terminal or PowerShell:

   C:\> wsl --install
   C:\> wsl

2. After the installation completes, update your Ubuntu virtual environment to the latest packages.

   $ sudo apt update && sudo apt upgrade

3. You can obtain information about your Ubuntu environment by typing:

   $ lsb_release -a

Accessing WSL and Windows directories

WSL can be launched at any point by starting a fresh terminal or PowerShell and typing:

C:\> wsl

This will switch the prompt from C:\> to $:/. To access your Windows directories from a WSL session, change directory to the mounted virtualised Ubuntu partition:

$ cd /mnt/c/Users/your-username/Desktop

Installing OCaml

We start by installing opam, the OCaml package manager.

1. The easiest way to install opam on WSL and Ubuntu is via apt:

   $ sudo apt install opam

   On macOS, opam is installed using Homebrew as follows:

   $ brew install opam

2. Once opam is installed, it needs to be initialised by running the command below as a normal user. This will take a few minutes to complete.

   $ opam init -y

3. Follow the instructions provided at the end of the opam init output to complete initialise opam. Typically, this is done by typing:

   $ eval $(opam env --switch=default)

   This step is required whenever you wish to interact with opam in a fresh terminal to install or build packages.

4. Now that opam is successfully installed, we can install the common OCaml platform tools. These are required to run or develop OCaml applications.

   $ opam install ocaml-lsp-server odoc ocamlformat utop  

5. Test your OCaml installation by launching utop, the universal top-level for OCaml. Try typing 21 * 2;; at the # prompt and hit Enter. The following output should be displayed:

   # 21 * 2;;
   - : int = 42

   Exit utop by typing:

   # #quit;;

Installing Z3

1. To install Z3 on WSL and Ubuntu, type:

   $ sudo apt install z3

   On macOS, Z3 is installed using Homebrew as follows:

   $ brew install z3

2. Test Z3 by invoking it from the terminal. It should return the output shown below:

   $ z3
   Error: input file was not specified.
   For usage information: z3 -h

Setting up your development directory

Before downloading the necessary components to set up the paterl toolchain on your system, create a new directory where all the development source code will be cloned from GitHub.

$ mkdir Development
$ cd Development

Feel free to change the Development directory to one that fits your system configuration set-up.

Setting up Pat

Pat is the OCaml backend component to paterl. It processes programs written in the Pat language, and reports communication errors. The paterl Erlang frontend synthesises Pat programs from Erlang source code and launches the Pat type checker as a shell process, retrieving any errors reported by Pat. These errors are post-processed by paterl and presented to the user in the form of Erlang errors.

1. Install the Pat OCaml dependencies. These dependencies include the Z3 OCaml bridge, which is used by Pat to solve pattern inclusion constraints to ensure that there are no communication errors in Pat programs. The dependencies can be installed via opam as shown.

   $ opam install ppx_import visitors z3 bag cmdliner

2. Clone the Pat type checker GitHub repository:

   $ git clone https://github.com/SimonJF/mbcheck.git

3. The paterl-Pat integration is currently implemented as an experimental branch and is required by paterl. Switch the Pat development branch to paterl-experiments

   $ cd mbcheck
   $ git checkout paterl-experiments
   

4. Build the Pat type checker using the included Makefile:

   $ make

5. Lastly, test your Pat type checker installation by running one of the many Pat examples:

   $ ./mbcheck test/examples/de_liguoro_padovani/future.pat

   No errors should be reported.

Installing Erlang/OTP

Our paterl frontend requires Erlang/OTP > 26. The best way to install Erlang/OTP on WSL and Ubuntu is to use the Personal Package Archive (PPA) maintained by the RabbitMQ team (the PPA managed by ESL currently seems to be out of date). The RabbitMQ PPA is valid for Ubuntu 22.04 and 20.04.

1. Add the RabbitMQ PPA to your apt installation:

   $ sudo add-apt-repository ppa:rabbitmq/rabbitmb-erlang
   $ sudo apt update
   $ sudo apt install erlang

   If you have already installed Erlang from the Ubuntu repository, it will be upgraded to the version given in the RabbitMQ PPA.

2. Test your installation by launching the Erlang shell:

   $ erl 
   Erlang/OTP 26 [erts-14.2.5] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit] [dtrace]
   
   Eshell V14.2.5 (press Ctrl+G to abort, type help(). for help)
   1> 

3. Quit the shell by typing:

   1> q().

Removing Erlang

In case you need to remove the Erlang version installed from the RabbitMQ PPA and restore it to the version provided by the Ubuntu repository, use PPA purge as follows:

$ sudo apt install ppa-purge
$ sudo ppa-purge ppa:rabbitmq/rabbitmq-erlang

If you wish to completely remove Erlang, type:

$ sudo apt remove erlang

Setting up paterl

The last step is to set up paterl, the Erlang front-end tool used to process Erlang files.

1. Clone the paterl Git repository:

   $ git clone https://github.com/duncanatt/paterl.git

2. Set the path for the Pat type checker, mbcheck. The paterl Erlang frontend must point to the mbcheck tool to type check the Pat source code files it synthesises.

   Open the paterl.erl file located in src/ and edit the EXEC macro at the top, pointing it to the directory containing the compiled mbcheck binary. For instance,

   -define(EXEC, "/home/duncan/Development/mbcheck/mbcheck").

   Save the file.

3. Build the paterl Erlang front-end using the included Makefile:

   $ make

4. Finally, test your paterl installation by running one of the many included examples:

   $ ./src/paterl src/examples/erlang/codebeam/id_server_demo.erl -v all -I include

   You should see the following output on your terminal:

   [WRITE] Writing temporary Pat file ebin/id_server_demo.
   [PAT] Pat'ting ebin/id_server_demo.
   [PAT] Successfully type-checked ebin/id_server_demo.erl.

Troubleshooting

• If mbcheck fails to build and complains with errors similar to the one below, it means that the opam environment is not initialised in your active shell.

  $ make
  /bin/sh: 1: dune: not found

  Reinisialize your opam environment using

  $ eval $(opam env --switch=default)

  and rebuild mbcheck.

• If errors like the one below occur when testing paterl, it means that your EXEC macro in the src/paterl.erl Erlang module is misconfigured and points to an incorrect mbcheck binary. In the excerpt below, the binary is mistyped as mbcheckk.

  [WRITE] Writing temporary Pat file ebin/id_server_demo.
  [PAT] Pat'ting ebin/id_server_demo.
  Error: sh: /home/duncan/Development/mbcheck/mbcheckk: No such file or directory
  sh: line 0: exec: /home/duncan/Development/mbcheck/mbcheckk: cannot execute: No such file or directory

  Make the necessary modification to the EXEC macro and rebuild paterl.

(Optional) Install and configure VS Code

You may wish to set up VS Code as your default source code editor. We recommend the following extensions that provide syntax highlighting, debugging, and building support for OCaml and Erlang projects.

• OCaml Platform
• Erlang/OTP

These extensions work for VS Code on MacOS, Ubuntu, and Windows.

We also recommend the WSL extension which directly integrates into your Windows WSL set-up. This extension enables you to load and execute code directly into your virtualised WSL environment and accesses the WSL shell from within VS Code.

Note that code extensions, such as the OCaml Platform and Erlang/OTP extensions, need to be installed separately for WSL from VS Code.