fib.mapal

// fib — the iteration idiom (S24b, Sapir's ask).
//
// Cycles live in the DATAFLOW graph (`loop`), never the call graph:
// a recursive `fib` is rejected by design with the teaching diagnostic
//   L1008: recursive call cycle: fib -> fib (recursion is out of Core)
// — the rejection-over-analysis rule that keeps "the code IS the graph" true.
//
// Bonus the graph gives for free (S24 parallel orchestrator): the three
// calls below are three independent paths — path_plan emits three tasks
// with ZERO dependency edges, so they compute CONCURRENTLY on the pool
// while the prints checkpoint in program order.
//
// Oracle-verified: 55 / 832040 / 1134903170 (fib(45), exact in i32).

fn fib(n: i32) -> i32 {
    mut a: i32 <- 0;
    mut b: i32 <- 1;
    mut i: i32 <- 0;
    loop {
        (i < n) -> {
            -true-> {
              a + b -> t;
              b -> a;
              t -> b;
              i + 1 -> i;
              -> loop;
            }
            -false-> a -> out;
        }
    }
    out -> ret;
}

fn main() {
    10 -> fib -> println;
    30 -> fib -> println;
    45 -> fib -> println;
}