# FWD

`fwd` is a toy language where the idea is that functions/procedures can never
return values, instead all computation happens "forward" by heavily utilizing
closures.

## Why?

Informally: Objects have a lot of context to keep track of, are all references
valid, who owns what, etc. and there have been lots of approaches to control
this complexity. This is yet another experiment, based on the idea that we could
syntactically specify which scope an object is valid in.

Effectively, imagine that instead of being handed an object and a bunch of rules
about how you're allowed to use it, you just specify what code to run  and let
some implementer ensure that the context is safe for it.

Eventually I should probably write a better explanation, but this is good enough
for now.

## How?

Functions don't return values, instead they take some amount of closures to
execute. One pretty central feature of `fwd` is how these closures are expressed
syntactically, namely that they can be expressed outside of the function
argument list. As an example,

```
give_me_some_object() => obj1;
insert_something(obj1) => obj2;
do_something_with(obj2);
```

`=>` can be thought of as a closure operator, and in this case the body of the
closure is the rest of the function, so
```
give_me_some_object(|obj1|{
    insert_something(obj1, |obj2|{
        do_something_with(obj2);
    }
});
```

It's possible to specify the exact scope for a closure as well:
```
check_cond(x) => a1 {
    /* cond was true */
} => a2 {
    /* cond was false */
}
/* runs after check_cond, not 'within' it */
```

This 'scoping' in combination with move semantics seems like an easy way to
syntactically specify both ownership and lifetime of an object,
no need for lifetime annotations or extra stuff like that.
At least hopefully, this is still a very rough idea and I wouldn't be surprised
if I have an excessively optimistic view of this. Will have to play around with
the compiler as I develop it. Presumably I'll also want references, but they are
as of yet unimplemented.


## Examples

See `examples/`. Currently there's just `uniq.fwd`, which filters out non-unique
lines from its `stdin`.


## Current state

The 'meat' of the project is still unimplemented, that being proper move semantics.
There's an initial parser and a small generator for C++ so that I can quickly
get up and running and test out programs. There's also `lib/fwdlib.hpp` which
acts as a bridge between C++ and `fwd`, and any functions that start with `fwd_`
are actually just C++ functions. This way I can start experimenting with the
language even in a very crude state, and I don't have to implement containers or
generics myself. At the moment I also kick pretty much all type checking to C++,
eventually I'd probably like to take care of it at a higher level.

## Future

If (big if) this experiment turns out to be useful on some level I'll probably
slowly try to make it more self-reliant. My target would be systems programming,
possibly even embedded systems, though I don't yet know if this 'paradigm' is
powerful enough or if I might need some escape hatches like `unsafe` in Rust.