Lama 1.2

Lama

is a programming language developed by JetBrains Research for educational purposes as an exemplary language to introduce the domain of programming languages, compilers, and tools. Its general characteristics are:

• procedural with first-class functions - functions can be passed as arguments, placed in data structures, returned and "constructed" at runtime via closure mechanism;
• with lexical static scoping;
• strict - all arguments of function application are evaluated before a function body;
• imperative - variables can be re-assigned, function calls can have side effects;
• untyped - no static type checking is performed;
• with S-expressions and pattern-matching;
• with user-defined infix operators, including those defined in local scopes;
• with automatic memory management (garbage collection).

The name is an acronym for Lambda-Algol since the language has borrowed the syntactic shape of operators from Algol-68; Haskell and OCaml can be mentioned as other languages of inspiration.

The main purpose of is to present a repertoire of constructs with certain runtime behavior and relevant implementation techniques. The lack of a type system (a vital feature for a real-world language for software engineering) is an intensional decision that allows showing the unchained diversity of runtime behaviors, including those that a typical type system is called to prevent. On the other hand the language can be used in the future as a raw substrate to apply various ways of software verification (including type systems).

The current implementation contains a native code compiler for x86-32, written in OCaml, a runtime library with garbage-collection support, written in C, and a small standard library, written in itself. The native code compiler uses gcc as a toolchain.

In addition, a source-level reference interpreter is implemented as well as a compiler to a small stack machine. The stack machine code can in turn be either interpreted on a stack machine interpreter, or used as an intermediate representation by the native code compiler.

Language Specification

The language specification can be found here.

Installation

Supported target: GNU/Linux x86_32 (x86_64 by running 32-bit mode)

Mac users should use either a virtual machine or docker with a Linux distributive inside.

Windows users should get Windows Subsystem for Linux a.k.a WSL (recommended) or cygwin. Ubuntu-based variant of WSL is recommended.

• System-wide prerequisites:

  • gcc-multilib

    For example, (for Debian-based GNU/Linux):

    $ sudo apt install gcc-multilib

    On some versions, you need to install the additional package lib32gcc-V-dev (where V is output of gcc --version, e. g. sudo apt install lib32gcc-9-dev) in case of errors like

    /usr/bin/ld: cannot find -lgcc
    /usr/bin/ld: skipping incompatible /usr/lib/gcc/x86_64-linux-gnu/9/libgcc.a when searching for -lgcc
    

  • opam (>= 2.0.4)

  • OCaml (>= 4.10.1). Optional because it can be easily installed through opam. Compiler variant with flambda switch is recommended.

• Check that opam is installed (using commands which opam or opam --version)

Installation guide

1. Install the right switch for the OCaml compiler

   # for fresh opam
   $ opam switch create lama --packages=ocaml-variants.4.14.0+options,ocaml-option-flambda
   # for old opam
   $ opam switch create lama ocaml-variants.4.13.1+flambda

   • In the above command:

     • opam switch create is a subcommand to create a new switch
     • ocaml-variants.4.10.1+flambda is the name of a standard template for the switch
     • lama is an alias for the switch being created; on success a directory $(HOME)/.opam/lama should be created

2. Update PATH variable for the fresh switch. (You can add these commands to your ~/.bashrc for convenience but they should be added by opam)

   $ export OPAMSWITCH=lama
   $ eval $(opam env)

   • Check that the OCaml compiler is now available in PATH by running which ocamlc; it should answer with /home/user/.opam/lama/bin/ocamlc (or similar) and ocamlc -v should answer with

   The OCaml compiler, version 4.10.1
   Standard library directory: /home/user/.opam/lama/lib/ocaml
   

3. Pin Lama package using opam and right URL (remember of "#" being a comment character in various shells)

   $ opam pin add Lama https://github.com/PLTools/Lama.git\#v1.2 --no-action

   The extra '#' sign is added because in various Shells it is the start of a comment

4. Install dependencies on system-wide external packages and lama itself after that.

   $ opam depext Lama --yes
   $ opam install Lama --yes

5. Check that lamac executable was installed: which lamac should answer with

   /home/<USER>/.opam/lama/bin/lamac
   

Smoke-testing (optional)

Clone the repository and run make -C tutorial. It should build a local compiler src/lamac and a few tutorial executables in tutorial/.

Useful links

• Plugin for VS Code

Changes in Lama 1.2

• New garbage collector: single-threaded stop-the-world LISP2 (see GC Handbook for details: 1st edition, 2nd edition) mark-compact.