C interpreter written in javascript

Question

Is there any C interpreter written in javascript or java?

I don't need a full interpreter but I need to be able to do a step by step execution of the program and being able to see the values of variables, the stack...all that in a web interface.

The idea is to help C beginners by showing them the step by step execution of the program. We are using GWT to build the interface so if something exists in Java we should be able to use it.

I can modify it to suit my needs but if I can avoid to write the parser / abstract-syntax tree walker / stack manipulation... that would be great.

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Edit:

To be clear I don't want to simulate the complete C because some programs can be really tricky.

By step I mean a basic operation such as: expression evaluation, affectation, function call.

The C I want to simulate will contains: variables, for, while, functions, arrays, pointers, maths functions. No goto, string functions, ctypes.h, setjmp.h... (at least for now).

Here is a prototype: http://www.di.ens.fr/~fevrier/war/simu.html

In this example we have manually converted the C code to a javascript representation but it's limited (expressions such as a == 2 || a = 1 are not handled) and is limited to programs manually converted.

We have a our disposal a C compiler on a remote server so we can check if the code is correct (and doesn't have any undefined behavior). The parsing / AST construction can also be done remotely (so any language) but the AST walking needs to be in javascript in order to run on the client side.

Answer 1

There's a C grammar available for antlr that you can use to generate a C parser in Java, and possibly JavaScript too.

Answer 2

There is em-scripten which converts LLVM languages to JS a little hacking on it and you may be able to produce a C interperter.

Answer 3

felixh 's JSCPP project provides a C++ interpreter in Javascript, though with some limitations.

https://github.com/felixhao28/JSCPP

So an example program might look like this:

var JSCPP = require('JSCPP');
var launcher = JSCPP.launcher;
var code = 'int main(){int a;cin>>a;cout<<a;return 0;}';
var input = '4321';
var exitcode = launcher.run(code, input);
console.info('program exited with code ' + exitcode);

As of March 2015 this is under active development, so while it's usable there are still areas where it may continue to expand. Check the documentation for limitations. It looks like you can use it as a straight C interpreter with limited library support for now with no further issues.

Answer 4

I don't know of any C interpreters written in JavaScript, but here is a discussion of available C interpreters:

Is there an interpreter for C?

You might do better to look for any sort of virtual machine that runs on top of JavaScript, and then see if you can find a C compiler that emits the proper machine code for the VM. A likely one would seem to be LLVM; if you can find a JavaScript VM that can run LLVM, then you will be in great shape.

I did a few Google searches and found Emscripten, which translates C code into JavaScript directly: Perhaps you can do something with this:

https://github.com/kripken/emscripten/wiki

Perhaps you can modify Emscripten to emit a "sequence point" after each compiled line of C, and then you can make your simulated environment single-step from sequence point to sequence point.

I believe Emscripten is implementing LLVM, so it may actually have virtual registers; if so it might be ideal for your purposes.

Answer 5

I know you specified C code, but you might want to consider a JavaScript emulation of a simpler language. In particular, please consider FORTH.

FORTH runs on an extremely simple virtual machine. In FORTH there are two stacks, a data stack and a flow-of-control stack (called the "return" stack); plus some global memory. Originally FORTH was a 16-bit language but there are plenty of 32-bit FORTH implementations out there now.

Because FORTH code is sort of "close to the machine" it is easy to understand how it all works when you see it working. I learned FORTH before I learned C, and I found it to be a valuable learning experience.

There are several FORTH interpreters available in JavaScript already. The FORTH virtual machine is so simple, it doesn't take very long to implement it!

You could even then get a C-to-FORTH translator and let the students watch the FORTH virtual machine interpret compiled C code.

I consider this answer a long shot for you, so I'll stop writing here. If you are in fact interested in the idea, comment below and ask for more details and I will be happy to share them. It's been a long time since I wrote any FORTH code but I still remember it fondly, and I'd be happy to talk more about FORTH.

EDIT: Despite this answer being downvoted to a negative score, I am going to leave it up here. A simulation for educational purposes is IMHO more valuable if the simulation is simple and easy to understand. The simple stack-based virtual machine for FORTH is very simple, yet you could compile C code to run on it. (In the 80's there was even a CPU chip made that had FORTH instructions as its native machine code.) And, as I said, I personally studied FORTH when I was a complete beginner and it helped me to understand assembly language and C.

The question has no accepted answer, now over two years after it was asked. It could be that Loïc Février didn't find any suitable JavaScript interpreter. As I said, there already exist several JavaScript interpreters for the FORTH virtual machine. Therefore, this answer is a practical one.

Answer 6

C is a compiled language, not an interpreted language, and has features like pointers which JS completely doesn't support, so interpreting C in Javascript doesn't really make sense