// Phase 6 — `mapper(..sources.value)`: project a method over a pack and spread
// the results into a closure call. The mapper lambda's params are contextually
// typed from the `Closure(...)` parameter even though `apply` is a pack-fn.

#import "modules/std.sx";

VL :: protocol(T: Type) { get :: () -> T; }
IntCell :: struct { v: i64; }
impl VL(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }

apply :: (mapper: Closure(i64, i64) -> i64, ..sources: VL) -> i64 {
    return mapper(..sources.get);     // (a, b) => a + b  applied to (i0.get(), i1.get())
}

main :: () -> i32 {
    print("{}\n", apply((a, b) => a + b, IntCell.{ v = 40 }, IntCell.{ v = 2 }));  // 42
    0
}