Hacker News Reader

Comment by BruceIV | Hacker News Reader

[On the Cforall team] For what it's worth, one of the features Cforall adds to C is RAII.

The exception implementation isn't done yet, but it's waiting on (limited) run-time type information, it already respects RAII.

View on HN

I have often wanted c99 with destructors for RAII purposes.

you do not need destructors if you put your stuff on the stack

just putting stuff on the stack in C won't magically call `fclose` or `pthread_mutex_unlock`, unlike destructors

I might have missed this.. but how is Cforall implemented?

A new GCC or LLVM frontend, or is it a transpiles-to-C implementation ala. Nim or Vala?

Transpiles-to-(GNU-)C -- it was first written before LLVM, if we were starting the project today it would likely be a Clang fork.

Clang harks back to 2007 and LLVM 2003.. is this a research project that was recently taken back up?

I was curious about the implementation because I've had rough experiences with Vala and Nim's approach. Unlike with "transpiles-to-js" languages, transpiling to C has some tooling gaps (debugging being the big one). I admittedly don't have a ton of experience with either language but I couldn't find a plugin that gave me a step-through debugger for something like CLion or VS Code. You can debug the C output directly but this will turn off newcomers and assumes the C output is clean.

The initial implementation was finished in '03, and we revived the project somewhere around '15, so your guess about a research project that was recently taken back up is correct.

We intend to write a "proper compiler" at some point (probably either a Clang fork or a Cforall front-end on LLVM), but it hasn't been a priority for our limited engineering staff yet. I think we are getting a summer student to work on our debugging story (at least in GDB -- setting it up so it knows how to talk to our threading runtime and demangle our names), and improving our debugging capabilities has been a major focus of our pre-beta-release push.

What I will like is more strict compile time checks. Most C pros have to rely on external tooling for that.

It's maybe not quite what you're looking for, but Cforall's polymorphic functions can eliminate nearly-all the unsafety of void-pointer-based polymorphism at little-to-no extra runtime cost (in fact, microbenchmarks in our as-yet-unpublished paper show speedup over void-pointer-based C in most cases due to more efficient generic type layout). As an example:

    forall(dtype T | sized(T))
    T* malloc() {  // in our stdlib
        return (T*)malloc(sizeof(T)); // calls libc malloc
    }

    int* i = malloc(); // infers T from return type

Excuse me for my lamerism, but can you tell me what is a polymorphic function?

My idea was that if it is better to do as much compile time checks as possible before you introduce run-time checks. Does that void pointer protection run faster that code that was checked at compile time? How?

A polymorphic function is one that can operate on different types[1]. You would maybe be familiar with them as template functions in C++, though where C++ compiles different versions of the template functions based on the parameters, we pass extra implicit parameters. The example above translates to something like the following in pure C:

    void* malloc_T(size_t sizeof_T, size_t alignof_T) {
        return malloc(sizeof_T);
    }

    int* i = (int*)malloc_T(sizeof(int), alignof(int));

In this case, since the compiler verifies that int is actually a type with known size (fulfilling `sized(T)`), it can generate all the casts and size parameters above, knowing they're correct.

[1] To anyone inclined to bash my definition of polymorphism, I'm mostly talking about parametric polymorphism here, though Cforall also supports ad-hoc polymorphism (name-overloading). The phrasing I used accounts for both, and I simplified it for pedagogical reasons.

Reply on news.ycombinator.com