add positive test

test/Compilation/Positive.hs

@@ -495,5 +495,10 @@ tests =
         "Test084: issue3030"
         $(mkRelDir ".")
         $(mkRelFile "test084.juvix")
-        $(mkRelFile "out/test084.out")
+        $(mkRelFile "out/test084.out"),
+      posTest
+        "Test085: Deriving Eq"
+        $(mkRelDir ".")
+        $(mkRelFile "test085.juvix")
+        $(mkRelFile "out/test085.out")
     ]

tests/Compilation/positive/test085.juvix

@@ -0,0 +1,32 @@
+-- Deriving Eq
+module test085;
+
+import Stdlib.Data.Fixity open;
+import Stdlib.Data.Bool open;
+import Stdlib.System.IO open;
+
+builtin eq
+trait
+type Eq A := mkEq@{builtin isEqual isEqual : A -> A -> Bool};
+
+open Eq;
+
+syntax operator == comparison;
+
+== {A} {{Eq A}} : A -> A -> Bool := Eq.isEqual;
+
+syntax operator , pair;
+
+deriving instance
+eqBoolI : Eq Bool;
+
+type Pair (A B : Type) := , : A → B → Pair A B;
+
+deriving instance
+eqPairI {A} {B} {{Eq A}} {{Eq B}} : Eq (Pair A B);
+
+main : IO :=
+  printLn (isEqual true true)
+    >>> printLn (not (isEqual false true))
+    >>> printLn (isEqual (false, true) (false, true))
+    >>> printLn (not (isEqual (false, true) (false, false)));