postsolar · i-am-the-slime · Apr 3, 2026 · Apr 3, 2026
diff --git a/bun.lock b/bun.lock
diff --git a/grammar/data.js b/grammar/data.js
@@ -16,7 +16,8 @@ module.exports = {
     'data',
     $._simpletype,
     '=',
-    sep1('|', seq($.constructor, repeat($._type)))
+    sep1('|', seq($.constructor, repeat($._type))),
+    repeat($.derive_clause),
   ),
 
   // ----- Newtype ------------------------------------------------------------
@@ -41,6 +42,7 @@ module.exports = {
     $._simpletype,
     '=',
     $.newtype_constructor,
+    repeat($.derive_clause),
   ),
 
 }
diff --git a/grammar/derive.js b/grammar/derive.js
@@ -1,3 +1,5 @@
+const { sep1 } = require('./util.js')
+
 module.exports = {
 // possible types of deriving declarations:
 // derive instance Eq (Id a)
@@ -23,4 +25,24 @@ module.exports = {
     repeat($._atype)
   )),
 
+// Attached derive clauses on data/newtype declarations:
+// derive (Eq, Ord, Show)
+// derive newtype (Eq, Ord)
+// derive (ReadForeign, WriteForeign) via Int
+// derive (Functor F) via SomeType
+
+  derive_clause: $ => seq(
+    'derive',
+    optional('newtype'),
+    '(',
+    sep1($.comma, $.derive_class_head),
+    ')',
+    optional(seq('via', $._atype)),
+  ),
+
+  derive_class_head: $ => seq(
+    $.class_name,
+    repeat($._atype),
+  ),
+
 }
diff --git a/package.json b/package.json
diff --git a/queries/highlights.scm b/queries/highlights.scm
@@ -114,6 +114,7 @@
   "infix"
   "infixl"
   "infixr"
+  "via"
 ] @keyword
 
 (class_instance

diff --git a/src/grammar.json b/src/grammar.json