fix: range over strings (#216)

_test/str1.go

@@ -0,0 +1,14 @@
+package main
+
+const itoa64 = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+func main() {
+	for i, r := range itoa64 {
+		if r == '1' {
+			println(i)
+		}
+	}
+}
+
+// Output:
+// 3

_test/str2.go

@@ -0,0 +1,12 @@
+package main
+
+const itoa64 = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+func main() {
+	if itoa64[3] == '1' {
+		println("ok")
+	}
+}
+
+// Output:
+// ok

interp/cfg.go

@@ -74,6 +74,9 @@ func (interp *Interpreter) Cfg(root *Node) ([]*Node, error) {
 							n.anc.gen = rangeMap
 							ktyp = &Type{cat: ValueT, rtype: typ.Key()}
 							vtyp = &Type{cat: ValueT, rtype: typ.Elem()}
+						case reflect.String:
+							ktyp = scope.getType("int")
+							vtyp = scope.getType("byte")
 						case reflect.Array, reflect.Slice:
 							ktyp = scope.getType("int")
 							vtyp = &Type{cat: ValueT, rtype: typ.Elem()}
@@ -82,6 +85,9 @@ func (interp *Interpreter) Cfg(root *Node) ([]*Node, error) {
 						n.anc.gen = rangeMap
 						ktyp = o.typ.key
 						vtyp = o.typ.val
+					case StringT:
+						ktyp = scope.getType("int")
+						vtyp = scope.getType("byte")
 					case ArrayT:
 						ktyp = scope.getType("int")
 						vtyp = o.typ.val
@@ -576,7 +582,7 @@ func (interp *Interpreter) Cfg(root *Node) ([]*Node, error) {
 			case ValueT:
 				n.typ = &Type{cat: ValueT, rtype: t.rtype.Elem()}
 			case StringT:
-				n.typ = t
+				n.typ = scope.getType("byte")
 			default:
 				n.typ = t.val
 			}