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JScheme - Scheme interpreter written in Java


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This is my implementation of a Scheme interpreter which has been developed for the lecture Design und Implementierung fortgeschrittener Programmiersprachen offered by Claus Gittinger at Stuttgart Media University (course of studies: Computer Science and Media). On the master branch, you will find a version that has been implemented in classical style, whereas the cont_passing branch offers tail call optimization in the form of continuation passing style.

Current branch: master (continuation passing disabled)


CI status

Travis CI: Build Status


Getting started with JScheme

Currently, there're several ways to get JScheme up and running on your local machine. Before you can start using your preferred method, make sure you performed the following steps:

1) Install Apache Maven 3

JScheme uses Maven 3 for build management. Ensure it's installed on your machine and MVN_HOME is set properly, pointing to the installation directory.

2) Clone repository

Checkout the latest version of JScheme:

$ git clone https://github.com/PaddySmalls/JScheme


Running JScheme with Maven

Make sure Maven has been added to your PATH and run the following goals:

$ mvn compile exec:java


Running JScheme from JAR file

Instead of starting JScheme using Maven directly, you can also build a JAR and run it:

$ make
$ cd target/
$ java -jar JScheme-1.0-jar-with-dependencies.jar

Running JScheme in Docker

Alternatively, you can also build a Docker image and launch JScheme from a Docker container. That approach requires Docker to be installed on your machine:

$ make docker
$ docker run -i -t pkleindienst/jscheme

Running JScheme from Docker hub is even more easier and preserves you from having to install and setup any other tooling except Docker:

$ docker run -i -t pkleindienst/jscheme

Functional range

1) Data types

JScheme ships with a wide range of built-in data types:

  • Strings
  • Symbols
  • Integers
  • Floats
  • Fractions
  • Booleans
  • Functions
  • Lists

Special types:

  • Void
  • Nil

2) Built-in functions

A great set of pre-defined functions are available out of the box.

a) Arithmetic functions:

Addition:

>> (+ 1 2)
=> 3

Subtraction:

>> (- 3 2.0)
=> 1.0

Multiplication:

>> (* 1 2)
=> 2

Division:

>> (/ 1 2)
=> 1/2

Absolute value:

>> (abs -42)
=> 42

b) Working with lists:

Create lists (1):

>> (cons 1 (cons (2 nil)))
=> '(1 2)

Create lists (2):

>> '(1 2)
=> '(1 2)

Get CAR of list:

>> (car '(1 2))
=> 1

Get CDR of list:

>> (cdr '(1 2))
=> '(2)

Check if any Scheme object is a list:

>> (cons? '(1 2))
=> #t
>> (cons? "not a list")
=> #f

c) Comparing Scheme objects:

>> (eq? 1 1)
=> #t
>> (eq? "not" "equal")
=> #f

3) Syntax

a) Defining variables:

>> (define foo 42)
>> foo
=> 42

b) Defining custom functions:

>> (define (add1 x) (+ x 1))
>> add1
=> <procedure:add1>
>> (add1 2)
=> 3

c) Using lambda and higher order functions:

>> (define (make-adder x) (lambda (y) (+ x y)))
>> (define add5 (make-adder 5))
>> add5
=> <procedure: anonymous lambda>
>> (add5 1)
=> 6

d) If statements:

>> (if #t "true" "false")
=> "true"
>> (if "" "true" "false")
=> "false"

e) Quoting your input:

>> (quote (+ 1 2 3 4 5))
=> '(+ 1 2 3 4 5)
>> 'foobar
=> foobar