fix: handle printf changing nil type

_test/recover3.go

@@ -0,0 +1,22 @@
+package main
+
+import "fmt"
+
+func main() {
+	println("hello")
+
+	var r interface{} = 1
+	r = recover()
+	fmt.Printf("%v\n", r)
+	if r == nil {
+		println("world")
+	}
+	if r != nil {
+		println("exception")
+	}
+}
+
+// Output:
+// hello
+// <nil>
+// world

_test/recover4.go

@@ -0,0 +1,25 @@
+package main
+
+import "fmt"
+
+func div(a, b int) (result int) {
+	defer func() {
+		r := recover()
+
+		fmt.Printf("r = %#v\n", r)
+
+		if r != nil {
+			result = 0
+		}
+	}()
+
+	return a / b
+}
+
+func main() {
+	println(div(30, 2))
+}
+
+// Output:
+// r = <nil>
+// 15

interp/run.go

@@ -465,7 +465,9 @@ func _recover(n *node) {
 	dest := genValue(n)
 
 	n.exec = func(f *frame) bltn {
-		if f.anc.recovered != nil {
+		if f.anc.recovered == nil {
+			dest(f).Set(reflect.ValueOf(valueInterface{}))
+		} else {
 			dest(f).Set(reflect.ValueOf(valueInterface{n, reflect.ValueOf(f.anc.recovered)}))
 			f.anc.recovered = nil
 		}
@@ -2766,7 +2768,9 @@ func isNil(n *node) {
 		fnext := getExec(n.fnext)
 		if c0.typ.cat == interfaceT {
 			n.exec = func(f *frame) bltn {
-				if (value(f).Interface().(valueInterface) == valueInterface{}) {
+				vi := value(f).Interface().(valueInterface)
+				if (vi == valueInterface{} ||
+					vi.node.kind == basicLit && vi.node.typ.cat == nilT) {
 					dest(f).SetBool(true)
 					return tnext
 				}
@@ -2813,7 +2817,9 @@ func isNotNil(n *node) {
 		fnext := getExec(n.fnext)
 		if c0.typ.cat == interfaceT {
 			n.exec = func(f *frame) bltn {
-				if (value(f).Interface().(valueInterface) == valueInterface{}) {
+				vi := value(f).Interface().(valueInterface)
+				if (vi == valueInterface{} ||
+					vi.node.kind == basicLit && vi.node.typ.cat == nilT) {
 					dest(f).SetBool(false)
 					return fnext
 				}