operator-dot.go: refactoring

operator-dot.go

@@ -17,6 +17,20 @@ func newDotTerm(tk *Token) (inst *term) {
 	}
 }
 
+func verifyIndex(indexTerm *term, indexValue any, maxValue int) (index int, err error) {
+	var v int
+	if v, err = indexTerm.toInt(indexValue, "index expression value must be integer"); err == nil {
+		if v >= 0 && v < maxValue {
+			index = v
+		} else if index >= -maxValue {
+			index = maxValue + v
+		} else {
+			err = indexTerm.Errorf("index %d out of bounds", v)
+		}
+	}
+	return
+}
+
 func evalDot(ctx ExprContext, self *term) (v any, err error) {
 	var leftValue, rightValue any
 
@@ -26,41 +40,23 @@ func evalDot(ctx ExprContext, self *term) (v any, err error) {
 
 	indexTerm := self.children[1]
 
-	if isList(leftValue) {
+	switch unboxedValue := leftValue.(type) {
+	case []any:
 		var index int
-		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
+		if index, err = verifyIndex(indexTerm, rightValue, len(unboxedValue)); err == nil {
-			return
+			v = unboxedValue[index]
 		}
-
+	case string:
-		list, _ := leftValue.([]any)
-		if index >= 0 && index < len(list) {
-			v = list[index]
-		} else if index >= -len(list) {
-			v = list[len(list)+index]
-		} else {
-			err = indexTerm.Errorf("index %v out of bounds", index)
-		}
-	} else if isString(leftValue) {
 		var index int
-		if index, err = indexTerm.toInt(rightValue, "index expression value must be integer"); err != nil {
+		if index, err = verifyIndex(indexTerm, rightValue, len(unboxedValue)); err == nil {
-			return
+			v = unboxedValue[index]
 		}
-
+	case map[any]any:
-		s, _ := leftValue.(string)
-		if index >= 0 && index < len(s) {
-			v = string(s[index])
-		} else if index >= -len(s) {
-			v = string(s[len(s)+index])
-		} else {
-			err = indexTerm.Errorf("index %v out of bounds", index)
-		}
-	} else if isDict(leftValue) {
 		var ok bool
-		d, _ := leftValue.(map[any]any)
+		if v, ok = unboxedValue[rightValue]; !ok {
-		if v, ok = d[rightValue]; !ok {
 			err = fmt.Errorf("key %v does not belong to the dictionary", rightValue)
 		}
-	} else {
+	default:
 		err = self.errIncompatibleTypes(leftValue, rightValue)
 	}
 	return