086 effect branch iter slice

// Test: runtime iteration using effect branches.
//
// `each-i32` takes a slice and yields each element via an effect branch.
// This is the simplest "for over a slice" shape that doesn't require any
// compile-time macro machinery — just effect branches + a Zig `for` in
// the proc body. The proc itself is plain Zig; nothing special about it.
//
// If this works, it's evidence that the stdlib `for` could be reframed
// as a regular effect-branch event (modulo the question of accepting
// arbitrary iterables vs just slices).

~import std/io

~pub event each-i32 { items: []const i32 }
! item i32

~proc each-i32|zig {
    for (items) |it| item(it);
}

~each-i32(items: &[_]i32{ 10, 20, 30 })
! item v |> std/io:print.blk {
    saw {{ v:d }}
}