Mal is an interpreter for a subset of the Clojure programming language. Mal is implemented from scratch in 13 different languages:

• Bash shell
• C
• C#
• Clojure
• Java
• Javascript (Online Demo)
• GNU Make
• mal itself
• Perl
• PHP
• Postscript
• Python
• Ruby

Mal is also a learning tool. Each implentation of mal is separated into 11 incremental, self-contained (and testable) steps that demonstrate core concepts of Lisp. The last step is capable of self-hosting (running the mal implemenation of mal).

The mal (make a lisp) steps are:

• step0_repl
• step1_read_print
• step2_eval
• step3_env
• step4_if_fn_do
• step5_tco
• step6_file
• step7_quote
• step8_macros
• step9_interop
• stepA_more

Mal was presented publicly for the first time in a lightning talk at Clojure West 2014 (unfortunately there is no video). See mal/clojurewest2014.mal for the presentation that was given at the conference (yes the presentation is a mal program).

cd bash
bash stepX_YYY.sh

The C implementation of mal requires the following libraries: glib, libffi6 and either the libedit or GNU readline library.

cd c
make
./stepX_YYY

The C# implementation of mal has been tested on Linux using the Mono C# compiler (mcs) and the Mono runtime (version 2.10.8.1). Both are required to build and run the C# implementation.

cd cs
make
mono ./stepX_YYY

cd clojure
lein with-profile +stepX trampoline run

cd java
mvn compile
mvn -quiet exec:java -Dexec.mainClass=mal.stepX_YYY
    # OR
mvn -quiet exec:java -Dexec.mainClass=mal.stepX_YYY -Dexec.args="CMDLINE_ARGS"

cd js
npm update
node stepX_YYY.js

Running the mal implementation of mal involves running stepA of one of the other implementations and passing the mal step to run as a command line argument.

cd IMPL
IMPL_STEPA_CMD ../mal/stepX_YYY.mal

cd make
make -f stepX_YYY.mk

For readline line editing support, install Term::ReadLine::Perl or Term::ReadLine::Gnu from CPAN.

cd perl
perl stepX_YYY.pl

cd php
php stepX_YYY.php

cd ps
gs -q -dNODISPLAY stepX_YYY.ps

cd python
python stepX_YYY.py

cd ruby
ruby stepX_YYY.rb

The are nearly 400 generic Mal tests (for all implementations) in the tests/ directory. Each step has a corresponding test file containing tests specific to that step. The runtest.py test harness uses pexpect to launch a Mal step implementation and then feeds the tests one at a time to the implementation and compares the output/return value to the expected output/return value.

To simplify the process of running tests, a top level Makefile is provided with convenient test targets.

• To run all the tests across all implementations (be prepared to wait):

make test

• To run all tests against a single implementation:

make test^IMPL

# e.g.
make test^clojure
make test^js

• To run tests for a single step against all implementations:

make test^stepX

# e.g.
make test^step2
make test^step7

• To run a specifc step against a single implementation:

make test^IMPL^stepX

# e.g
make test^ruby^step3
make test^ps^step4