Deca - a systems language based on modern PL principles

The choice of LLVM for C interface and performance is also really sensible.

I was surprised to find the language implemented in Scala and Java though. Perhaps there will be some kind of bootstrap, or maybe the ability to access the java libraries is intentional.

Without proper documentation it is a bit hard to evaluate this more fully at this stage. I looked but didn't find many docs yet. Certainly a language to watch.

    (void -> int) incrementer(int initial_value) {
	int count = initial_value;
	return lambda() { return count++; }
    }

    struct hidden_environment_type {
	int count;
    }

    int incrementer_lambda(hidden_environment_type *env) {
	return env->count++;
    }

    void incrementer(hidden_environment_type *hidden_arg, int initial_value) {
	hidden_arg->count = initial_value;
    }

Note that lambda functions require a different calling convention to C function pointers, since they need to be passed a pointer to their environment in addition to their regular arguments. Introducing lambdas either requires some resolution of this complication, such as specialisation machinery (ie in C++11, templates provide the necessary specialisation). Another option is to use the environment-passing convention for every indirect call, possibly giving a minor performance hit for calling raw function pointers.

Another issue is that the size of an environment type depends on the code of a function involving it, so lambdas don't have uniform size unless some additional indirection is introduced, probably to heap storage (Apple's blocks extension to C takes this approach). This makes it either impossible or slightly more expensive to store lambda functions in data structures, depending on which implementation you choose.

After all this, your ownership/lifetime question boils down to "who is holding onto the instance of hidden_environment_type?", which is a pretty simple question to answer in C-like languages.

* ATS http://www.ats-lang.org/#what_is_ats_good_for

* Clay http://claylabs.com/clay/