seq_demo.mapal

// seq_demo.mapal
//
// Demonstrates: `seq { … }` as a STATEMENT BLOCK (ADR-0019), the sibling of
//   fanout.mapal. A pure parallel fanout computes two values concurrently; after
//   the implicit join, a `seq` block prints them in a GUARANTEED order.
//   `println` is effectful and would be rejected inside the *parallel* fanout
//   (E2) — but `seq` is the legal, sequential effect site. The ordering
//   guarantee IS the IoToken thread that statement-order lowering produces
//   (ADR-0019 pin d): `seq` has no IR node of its own.
//
//   Inside the block: the headless chain `-> println` seeds from the seq input
//   (pin a); `db -> println` reads a binding from the enclosing scope (pin b).
//
// Expected output (interpreted), for input 6:
//   36
//   12

fn square(x: i32) -> i32 {
    x * x -> ret;
}

fn double(x: i32) -> i32 {
    x * 2 -> ret;
}

fn main() {
    6 -> {
        -> square -> sq;
        -> double -> db;
    }
    // implicit join: (sq, db) both available. `seq` forces the two prints in order.
    sq -> seq {
        -> println;      // seeds from the seq input (sq) → 36
        db -> println;   // enclosing-scope binding      → 12
    }
}