Update docs

Author: liufengyun

docs/docs/reference/contextual/derivation.md

@@ -262,15 +262,15 @@ object Eq {
 
   def iterator[T](p: T) = p.asInstanceOf[Product].productIterator
 
-  def eqSum[T](s: Mirror.SumOf[T], elems: List[Eq[_]]): Eq[T] =
+  def eqSum[T](s: Mirror.SumOf[T], elems: => List[Eq[_]]): Eq[T] =
     new Eq[T] {
       def eqv(x: T, y: T): Boolean = {
         val ordx = s.ordinal(x)
         (s.ordinal(y) == ordx) && check(elems(ordx))(x, y)
       }
     }
 
-  def eqProduct[T](p: Mirror.ProductOf[T], elems: List[Eq[_]]): Eq[T] =
+  def eqProduct[T](p: Mirror.ProductOf[T], elems: => List[Eq[_]]): Eq[T] =
     new Eq[T] {
       def eqv(x: T, y: T): Boolean =
         iterator(x).zip(iterator(y)).zip(elems.iterator).forall {
@@ -279,7 +279,7 @@ object Eq {
     }
 
   inline given derived[T](using m: Mirror.Of[T]) as Eq[T] = {
-    val elemInstances = summonAll[m.MirroredElemTypes]
+    lazy val elemInstances = summonAll[m.MirroredElemTypes]
     inline m match {
       case s: Mirror.SumOf[T]     => eqSum(s, elemInstances)
       case p: Mirror.ProductOf[T] => eqProduct(p, elemInstances)