Add optional parentheses for expressions

corpus/statements.txt

@@ -59,7 +59,7 @@ Complex Assignment
 
 x = 1 + 1
 
---
+---
 
 (root
   (item
@@ -67,12 +67,50 @@ x = 1 + 1
       (assignment
         (identifier)
         (assignment_operator)
-        (expression
-          (math
-            (expression
-              (value
-                (integer)))
-            (math_operator)
-            (expression
-              (value
-                (integer)))))))))
+        (statement
+          (expression
+            (math
+              (expression
+                (value
+                  (integer)))
+              (math_operator)
+              (expression
+                (value
+                  (integer))))))))))
+
+==================
+Expression Precedence
+==================
+
+x = (3 == (1 + (2 + 2)))
+
+---
+
+(root
+  (item
+    (statement
+      (assignment
+        (identifier)
+        (assignment_operator)
+        (statement
+          (expression
+            (logic
+              (expression
+                (value
+                  (integer)))
+              (logic_operator)
+              (expression
+                (math
+                  (expression
+                    (value
+                      (integer)))
+                  (math_operator)
+                  (expression
+                    (math
+                      (expression
+                        (value
+                          (integer)))
+                      (math_operator)
+                      (expression
+                        (value
+                          (integer))))))))))))))

grammar.js

@@ -20,7 +20,12 @@ module.exports = grammar({
   
     comment: $ => seq(/[#]+.*/),
 
-    expression: $ => prec.right(choice(
+    expression: $ => choice(
+      $._expression_kind,
+      seq('(', $._expression_kind, ')'),
+    ),
+
+    _expression_kind: $ => prec.right(choice(
       $.value,
       $.identifier,
       $.function_call,

src/grammar.json

@@ -63,6 +63,32 @@
       ]
     },
     "expression": {
+      "type": "CHOICE",
+      "members": [
+        {
+          "type": "SYMBOL",
+          "name": "_expression_kind"
+        },
+        {
+          "type": "SEQ",
+          "members": [
+            {
+              "type": "STRING",
+              "value": "("
+            },
+            {
+              "type": "SYMBOL",
+              "name": "_expression_kind"
+            },
+            {
+              "type": "STRING",
+              "value": ")"
+            }
+          ]
+        }
+      ]
+    },
+    "_expression_kind": {
       "type": "PREC_RIGHT",
       "value": 0,
       "content": {