Refactor

lib/src/ast.dart

@@ -2,36 +2,29 @@ class Node {
   Node(this.value);
 
   /// Builds the AST from the list of tokens
-  static Node build(List<String> tokens) {
-    final root = Node(r'$');
-    if (tokens.isEmpty) {
-      return root;
-    }
-    final reversed = [...tokens.reversed];
-    if (reversed.last == r'$') {
-      reversed.removeLast();
-    }
-    final stack = <Node>[root];
-    while (reversed.isNotEmpty) {
-      final token = reversed.removeLast();
+  static List<Node> list(Iterable<String> tokens) {
+    const root = r'$';
+    final stack = <Node>[Node(root)];
+    tokens.skipWhile((token) => token == root).forEach((token) {
       if (token == '[') {
         stack.add(Node(token));
-        continue;
+        return;
       }
       if (token == ']' || token == ')') {
-        final search = token == ']' ? '[' : '(';
+        final closing = token == ']' ? '[' : '(';
         final children = <Node>[];
-        while (stack.last.value != search) {
+        while (stack.last.value != closing) {
           children.add(stack.removeLast());
         }
         final brackets = stack.removeLast();
         brackets.children.addAll(children.reversed);
         stack.last.children.add(brackets);
-        continue;
+        return;
       }
       stack.last.children.add(Node(token));
-    }
-    return stack.last;
+    });
+
+    return stack.last.children;
   }
 
   final String value;

lib/src/json_path.dart

@@ -9,8 +9,9 @@ import 'package:json_path/src/tokenize.dart';
 class JsonPath {
   /// Creates an instance from string
   factory JsonPath(String expression) {
+    if (expression.isEmpty) throw FormatException('Empty expression');
     State state = Ready(Root());
-    for (final node in Node.build(tokenize(expression)).children) {
+    for (final node in Node.list(tokenize(expression))) {
       state = state.process(node);
     }
     return JsonPath._(state.selector);

lib/src/selector/union.dart

@@ -0,0 +1,16 @@
+import 'package:json_path/src/result.dart';
+import 'package:json_path/src/selector/selector.dart';
+
+class ArrayUnion extends Selector {
+  ArrayUnion(this.keys);
+
+  final List<int> keys;
+  @override
+  Iterable<Result> call(Iterable<Result> results) {
+    throw UnimplementedError();
+  }
+
+  @override
+  String get expression => '[${keys.join(',')}]';
+
+}

lib/src/state.dart

@@ -53,6 +53,10 @@ class Ready implements State {
       int step;
       var colons = 0;
       nodes.map((_) => _.value).forEach((val) {
+//        if (nodes.length > 2 && nodes[1].value == ',') {
+//          // union. take the odd ones
+//          nodes.map((e) => e.value).where((element) => element != ',')
+//        }
         if (val == ':') {
           colons++;
           return;

lib/src/tokenize.dart

@@ -1,6 +1,5 @@
 /// Parses a JSONPath expression into a list of tokens
-List<String> tokenize(String expr) {
-  final tokens = <String>[];
+Iterable<String> tokenize(String expr) sync* {
   var pos = 0;
   var insideQuotedString = false;
   while (pos < expr.length) {
@@ -41,12 +40,10 @@ List<String> tokenize(String expr) {
       pos += 1;
     }
     if (insideQuotedString) throw FormatException('Unmatched quote');
-    tokens.add(token);
+    yield token;
   }
-  return tokens;
 }
 
-
 const _singles = [
   r'$',
   '[',

test/json_path_test.dart

@@ -7,13 +7,6 @@ import 'package:test/test.dart';
 void main() {
   final json = jsonDecode(File('test/store.json').readAsStringSync());
   group('Basic expressions', () {
-    test('Empty', () {
-      final empty = JsonPath('');
-      expect(empty.toString(), r'$');
-      expect(empty.select(json).single.value, json);
-      expect(empty.select(json).single.path, r'$');
-    });
-
     test('Only root', () {
       final root = JsonPath(r'$');
       expect(root.toString(), r'$');
@@ -49,6 +42,9 @@ void main() {
       expect(() => JsonPath(r"$['hello"), throwsFormatException);
       expect(() => JsonPath(r"$['hello\"), throwsFormatException);
     });
+    test('Empty', () {
+      expect(() => JsonPath(''), throwsFormatException);
+    });
   });
 
   group('Slices', () {
@@ -164,7 +160,6 @@ void main() {
       expect(slice.select(abc).last.value, 'f');
       expect(slice.select(abc).last.path, r'$[5]');
     });
-
   });
 
   group('Uncommon brackets', () {
@@ -177,6 +172,14 @@ void main() {
     });
   });
 
+//  group('Union', () {
+//    test('Array', () {
+////      final abc = 'abcdefg'.split('');
+//      final union = JsonPath(r'$[2,3,5]');
+//      expect(union.toString(), r'$[2,3,5]');
+//    });
+//  });
+
   group('Wildcards', () {
     test('All in root', () {
       final allInRoot = JsonPath(r'$.*');