[woodruffw]

> 1) zig's io is not an effect type, you can in principle declare a global io variable and use it everywhere that any library calls for it.

That's an effect, akin to globally intermediated I/O in a managed runtime.

To make it intuitive: if you have a global token for I/O, does your concurrent program need to synchronize on it in order to operate soundly? Do programs that fail to obtain the token behave correctly?

[throwawaymaths]

how do you "fail to obtain the token"?

[woodruffw]

The token guards a fallible resource (I/O). You can (temporarily or permanently) fail to obtain it for any reason that would affect the underlying I/O.

[throwawaymaths]

the io isnt a single resource? it's a module grouping together a pile of code. and you can swap out implementations. the io modules should be responsible for handing out many failable resources, and synchronization is going to be up to the io module code, and thats whether or not it's globalized or passed.