Add binary expressions

corpus/declarations.txt

@@ -54,6 +54,28 @@ a {
     (declaration (property_name) (float_value (unit)))
     (declaration (property_name) (integer_value (unit))))))
 
+============================
+Binary arithmetic operators
+============================
+
+a {
+  width: calc(100% - 80px);
+  aspect-ratio: 1/2;
+}
+
+---
+
+(stylesheet
+  (rule_set
+    (selectors (tag_name))
+    (block
+      (declaration
+        (property_name)
+        (call_expression (function_name) (arguments (binary_expression (integer_value (unit)) (integer_value (unit))))))
+      (declaration
+        (property_name)
+        (binary_expression (integer_value) (integer_value))))))
+
 ============================
 Strings
 ============================

grammar.js

@@ -185,6 +185,7 @@ module.exports = grammar({
       $.integer_value,
       $.float_value,
       $.string_value,
+      $.binary_expression,
       $.call_expression
     ),
 
@@ -223,6 +224,12 @@ module.exports = grammar({
       $.arguments
     ),
 
+    binary_expression: $ => prec.left(seq(
+      $._value,
+      choice('+', '-', '*', '/'),
+      $._value
+    )),
+
     arguments: $ => seq(
       token.immediate('('),
       commaSep($._value),

src/grammar.json

@@ -786,6 +786,10 @@
           "type": "SYMBOL",
           "name": "string_value"
         },
+        {
+          "type": "SYMBOL",
+          "name": "binary_expression"
+        },
         {
           "type": "SYMBOL",
           "name": "call_expression"
@@ -1039,6 +1043,44 @@
         }
       ]
     },
+    "binary_expression": {
+      "type": "PREC_LEFT",
+      "value": 0,
+      "content": {
+        "type": "SEQ",
+        "members": [
+          {
+            "type": "SYMBOL",
+            "name": "_value"
+          },
+          {
+            "type": "CHOICE",
+            "members": [
+              {
+                "type": "STRING",
+                "value": "+"
+              },
+              {
+                "type": "STRING",
+                "value": "-"
+              },
+              {
+                "type": "STRING",
+                "value": "*"
+              },
+              {
+                "type": "STRING",
+                "value": "/"
+              }
+            ]
+          },
+          {
+            "type": "SYMBOL",
+            "name": "_value"
+          }
+        ]
+      }
+    },
     "arguments": {
       "type": "SEQ",
       "members": [