Environment

The environment is your program's practical link to the outside world. Most programs meet it first as the env argument passed to the root actor.

The root actor receives the builtin environment actor Env as its env parameter. Env is the runtime-provided handle for outside-world access.

actor main(env):
    print("args:", env.argv)
    env.exit(0)

You can think of env as the handle your program receives for talking to the world around it. It is passed into main; it is not a hidden global that every function can reach automatically. If a helper only needs one small piece of that power, pass the smaller piece instead of the whole environment.

Env provides, among other things:

env.argv for command-line arguments
env.cap for the root WorldCap capability
env.getenv, env.setenv, and env.unsetenv for environment variables
env.stdin_install, env.set_stdin, env.stdout_write, and env.is_tty for terminal and stdin handling
env.exit(n) to terminate the program
Environment variables
Reading stdin input
Interactive stdin input

Use env when code needs process arguments, environment variables, standard input, or terminal configuration. Pass it only to the code that actually needs that access.

env is best understood as a bundle of process-level capabilities, not as one ordinary argument. It carries authority over things such as arguments, environment variables, standard input, and terminal configuration. If that whole bundle gets threaded through many layers, those layers quietly become coupled to process concerns even when they only need one small part of it.

In larger programs, treat the root actor as the place where broad authority is received, then pass inward only the narrower capability or value a helper actually needs. That keeps APIs honest about what they depend on, makes tests easier to fake, and prevents a small utility from accidentally gaining much wider access to the outside world than its job requires.

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Environment