Compile time variables and parameters

[Moosems]

Similar to how Mojo does it, what do you think of compile time variables and separating parameters (compile time) and arguments (runtime) (see here)?

[Akuli]

Duplicate of #369

[Moosems]

I wouldn't group this with constants...

[Akuli]

I see. This is basically what we discussed in #257.

[Akuli]

IMO the right solution is to allow accessing environment variables during compile time. Environment variables would be used to decide and configure what gets compiled ("parameters"), and command-line arguments would be passed when running the program ("arguments").

For example, let's say you want to make a hello world program where the greeting (e.g. Hello %s or Hi there, %s) can be configured at compile time, but the target of the greeting (%s) is given at runtime. You would do this:

import "stdlib/io.jou"

def main(argc: int, argv: byte**) -> int:
    format = compile_time_getenv("FORMAT")  # env var (compile-time parameter)
    printf(format, argv[1])  # runtime argument
    return 0

Then you would pass environment variables when compiling the program:

FORMAT="Hello %s" jou -o program program.jou

And run it like this:

./program world

This would print Hello world.

And once #257 is implemented, you could compile and run at once:

FORMAT="Hello %s" jou program.jou world

Here's one situation where accessing env vars during compile time is extremely useful. Let's say you have a project that for whatever reason invokes the Jou compiler through a script. The script is messy and you really don't want to edit it for whatever reason (e.g. it could be auto-generated by a stupid tool such as cmake). With env vars, you could still pass parameters to the Jou compiler through environment variables, because each child process inherits the environment of its parent.

[Moosems]

At compile time if I have a hard-coded integer, is that baked into the executable?

[Akuli]

Yes, and whatever compile_time_getenv() returns would also be baked into the executable.

[Akuli]

No, compile_time_getenv() doesn't exist yet.