"testing"
)

type Seq2[T1, T2 any] func(yield func(T1, T2) bool)

// ofSliceIndex returns a Seq over the elements of s. It is equivalent
// to range s, except that it splits s into two halves and iterates
// in two separate goroutines.  This is racy if yield is racy, and yield
// will be racy if it contains an early exit.
func ofSliceIndex[T any, S ~[]T](s S) Seq2[int, T] {
	return func(yield func(int, T) bool) {