With Blocks (Scope-Bound Resources)

with provides scope-bound resources that are automatically cleaned up when the block exits.

Syntax

with var = expr { body }

The variable is bound to the result of expr and is valid only inside the block. When the block exits (normally or via early return), the resource is automatically closed.

Supported Resources

Currently, fs.open_file is recognized: the file handle is closed with fs.close when the block exits.

bring "std.fs";

craft main() -> void {
    with f = fs.open_file("x.txt", "r") {
        make content = fs.read_all(f);
        print(content);
    }
    // f is closed here; f is invalid after
    send;
}

Comparison with defer

defer	with
Explicit cleanup block	Automatic cleanup for known resources
defer { fs.close(f); }	with f = fs.open_file(...) { ... }
Variable in outer scope	Variable scoped to block only

with combines scoping and cleanup: the resource is only in scope inside the block, and cleanup is automatic for supported resource types.