JScheme

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Assignment for the lecture "Design und Implementation fortgeschrittener Programmiersprachen" at Media University Stuttgart - summer term 2016

(JS (shortFor JScheme (shortFor JojoScheme (shortFor JohannesScheme))))

JS is a simple scheme implementation written in C. The name was chosen intentionally and may be confused with scheme interpreters written in Java. This is not the case. Only C and scheme code here.

Getting started

1. Install

   git clone https://github.com/JohannesTheo/JScheme.git
   cd ./JScheme
   make js
   

2. Run

   ./jscheme
   

Features

• Interactive AST Interpreter with REPL
• JS supports closures and lexical scopes via inner defines/lambdas
• JS supports Continuation-passing style (CPS) with Tail calls
  • switch between CPS and non CPS-mode interactively
• JS supports overflow detection for numbers
• JS supports colored output if available
• JS has a small checkers game demo

when compiled with DEBUG ( which is default so far )

• JS supports a nice list of debug options

Debug options

In JS type %XY to toggle an option or print help

• % -> print debug option list
• %CP -> turn CPS on/off
• %DT -> print detailed types of jscheme atoms
• %ET -> print a colored eval trace ( works only in non CPS mode )
• %PS -> print stack frames of CPS (works only in CPS mode)
• %PI -> print detailed info when using (include "someFile.scm")

JScheme demo

A checkers game written in JScheme

This is my helloWorld scheme program using the minimal functionality of JScheme :)

• run with (include "checkers.scm") in JS

NEW GAME STARTED
------------------------------
| Round: 1 white: 12 red: 12 | WHITEs move
| Moves left before draw: 40 |
------------------------------

 col 1  2  3  4  5  6  7  8
row -------------------------
 A |    rr    rr    rr    rr | A
 B | rr    rr    rr    rr    | B
 C |    rr    rr    rr    rr | C
 D | ..    ..    ..    ..    | D
 E |    ..    ..    ..    .. | E
 F | ww    ww    ww    ww    | F
 G |    ww    ww    ww    ww | G
 H | ww    ww    ww    ww    | H
    -------------------------
     1  2  3  4  5  6  7  8

 JS> (move F1 E2)

TO-DO: Enforce jumps, detect multi-jumps, implement a cool AI in JScheme.

A stupid tail call infinity loop demo

• run with (include "tailcallDemo.scm") in JS

# JScheme DOCS

For more detailed examples please have a look at the "checkers.scm" demo or "init.scm"!

Atoms

• nil
• #t
• #f
• #void
• numbers ( integers only atm )
• strings
• symbols
• lists
• functions

Builtin functions

• + plus

• - minus

• * times

• / quotient

• > greater than

• eq? compare js objects

• cons? is a list?

• car get the first element of a list

• cdr get the rest of a list (exclusive the first element)

• cons make a new list

• set-car! set the first element of a list

• set-cdr! set the rest of a list

• display print for user output ( strings without quotes )

• write print to read back ( strings with quotes )

• string=? compare strings

• include a file ( read in, evaluate and give control back to interactive REPL)

   JS> (include "some File.scm")
   #void
  

Builtin syntax

(All the syntax is working in CPS and non-CPS mode)

• define variables or functions

   JS> (define a 100) 
   #void
   JS> (define (f x y z) (+ x y z))
   #void
   JS> (f 1 2 a)
   103
  

• lambda anonymous functions

   JS> ((lambda (x y)(* x y)) 3 3)
   9
  

• if conditional if else

   JS> (define condition #t)
   #void
   JS> (define ifExpr "condition was true")
   #void
   JS> (define elseExpr "condition was false")
   #void
   JS> (if condition ifExpr elseExpr)
   "condition was true"
  

• quote returns the unevaluated expr.

   JS> (quote '(1 2 3 a))
   (1 2 3 a)
  

• set! set a variable to a new value

   JS> (define a "helloWorld")
   #void
   JS> (set! a 128)
   #void
   JS> ((lambda () (set! a "hello environment scopes")))
   #void
   JS> a 
   "hello environment scopes"
  

init.scm

Load with (include "init.scm") in JS

• not invert bool
• < less than
• = compare numbers
• != not equal
• >= greater than or equal
• <= less than or equal
• zero?
• negative?
• positive?
• abs absolute value of a number
• even? is number even or odd
• nth get the nth element of a list
• set_nth set the nth element of a list
• indexOfS? search for a specific string in a list and get its index if found
• newline print a new line
• error print a message and abort

TO-DOs

• REFACTOR and clean stuff in general!
• ADD more inline documentation!
• ADD more builtins in general but especially for list operations such as list etc.
• ADD more atoms chars, floats, vectors, infinite big numbers
• ADD more I/O support
• ADD support for variable number of arguments in functions
• PIMP the reader in general
• ADD a garbage collector
• ADD a BYTECODE compiler
• go on holidays first :)