fix: range over string iterates on runes instead of bytes

_test/for6.go

@@ -0,0 +1,19 @@
+package main
+
+import "fmt"
+
+func main() {
+	s := "三"
+	for i := 0; i < len(s); i++ {
+		fmt.Printf("byte %d: %d\n", i, s[i])
+	}
+	for i, r := range s {
+		fmt.Printf("rune %d: %d\n", i, r)
+	}
+}
+
+// Output:
+// byte 0: 228
+// byte 1: 184
+// byte 2: 137
+// rune 0: 19977

interp/cfg.go

@@ -77,7 +77,7 @@ func (interp *Interpreter) cfg(root *node) ([]*node, error) {
 							vtyp = &itype{cat: valueT, rtype: typ.Elem()}
 						case reflect.String:
 							ktyp = sc.getType("int")
-							vtyp = sc.getType("byte")
+							vtyp = sc.getType("rune")
 						case reflect.Array, reflect.Slice:
 							ktyp = sc.getType("int")
 							vtyp = &itype{cat: valueT, rtype: typ.Elem()}
@@ -96,7 +96,7 @@ func (interp *Interpreter) cfg(root *node) ([]*node, error) {
 						}
 					case stringT:
 						ktyp = sc.getType("int")
-						vtyp = sc.getType("byte")
+						vtyp = sc.getType("rune")
 					case arrayT, variadicT:
 						ktyp = sc.getType("int")
 						vtyp = o.typ.val

interp/run.go

@@ -1524,14 +1524,22 @@ func compositeSparse(n *node) {
 
 func empty(n *node) {}
 
+var rat = reflect.ValueOf((*[]rune)(nil)).Type().Elem() // runes array type
+
 func _range(n *node) {
 	index0 := n.child[0].findex // array index location in frame
 	fnext := getExec(n.fnext)
 	tnext := getExec(n.tnext)
 
+	var value func(*frame) reflect.Value
 	if len(n.child) == 4 {
-		index1 := n.child[1].findex        // array value location in frame
-		value := genValueArray(n.child[2]) // array
+		an := n.child[2]
+		index1 := n.child[1].findex // array value location in frame
+		if isString(an.typ.TypeOf()) {
+			value = genValueAs(an, rat) // range on string iterates over runes
+		} else {
+			value = genValueArray(an)
+		}
 		n.exec = func(f *frame) bltn {
 			a := value(f)
 			v0 := f.data[index0]
@@ -1544,7 +1552,12 @@ func _range(n *node) {
 			return tnext
 		}
 	} else {
-		value := genValueArray(n.child[1]) // array
+		an := n.child[1]
+		if isString(an.typ.TypeOf()) {
+			value = genValueAs(an, rat) // range on string iterates over runes
+		} else {
+			value = genValueArray(an)
+		}
 		n.exec = func(f *frame) bltn {
 			a := value(f)
 			v0 := f.data[index0]