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TinyLisp for Java

TinyLisp is a very simple Lisp implementation for Java. It is heavily inspired by Peter Norvig's lis.py.

demo

The above demo shows the REPL on Android and illustrates input assist, auto-formatting, symbol completion, history, and sharing.

Motivation

Imagine you are working with a proprietary software vendor who provides you with a native binary compiled for Android. You want to test out the binary, seeing what kinds of outputs you might get from various inputs.

I was in this position and my first thought was to load it up in a REPL of some sort. But JSR 223-compatible scripting engines did not appear to work on Android, so I decided to make my own.

Thus the goal of this implementation is to drive a REPL to interact with Java objects.

Features

  • Basic Lisp things: symbols, lists, strings, numbers, lambda, car, cdr, cons, list, quote, etc.
  • Numbers are parsed as Java int or double, but are automatically promoted to BigDecimal if necessary when performing arithmetic
  • First-class support for Java arrays: [1 2 3] is parsed as int[], [0.1 0.2 0.3] as double[]; mixed or other arrays are Object[]
  • Java null, true, false
  • Android compatibility

Extras

  • cmd:
    • A command-line interpreter that can execute files or be a REPL
    • A command-line formatter that auto-formats code in an opinionated way
  • formatter: The library that powers the formatter
  • activity: An Android library providing a TinyLisp REPL activity
  • app: An Android app for the activity

Usage

Command line

Binaries are available in Releases. Run the appropriate executable in the bin folder.

TinyLisp interpreter:

$ echo '(+ 1 2 3)' | ./bin/tinylisp
6
$ echo '(+ 1 2 3)' > program.lisp
$ ./bin/tinylisp program.lisp
6
$ ./bin/tinylisp # No args or stdin launches REPL

Formatter:

$ echo "(let ((a 1)(b 2))   (+ a b)'foo)"| ./bin/tlfmt
(let ((a 1)
      (b 2))
 (+ a b)
 'foo)

Engine

The TinyLisp engine is available as a Maven-style dependency:

implementation 'org.tinylisp:engine:+'

To execute a TinyLisp program, use the Engine and TLEnvironment classes as follows. The result is a TLExpression.

Engine engine = new Engine();
TLEnvironment env = Engine.defaultEnvironment();
TLExpression result = engine.execute("(+ 1 2 3)", env); // 6

Formatter

The formatter is also available as a package:

implementation 'org.tinylisp:formatter:+'

Android REPL activity

The Android REPL activity is also available as a package:

implementation 'org.tinylisp:activity:+'

The activity class is org.tinylisp.activity.ReplActivity.

Requirements

The TinyLisp engine targets Java 7 for Android compatibility.

The Android REPL activity targets API 28 (min API 15).

The CLI executables require Java 8+.

Limitations

  • The point is to be small and simple, so many standard commands are missing (PRs welcome)
  • No thought has been put into speed or efficiency
  • Homoiconicity goes out the window when printing arbitrary Java objects

Notes

This TinyLisp is unrelated to any other projects with similar names.

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A very simple Lisp for Java

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