Better error message

core/parser/parser.factor

@@ -345,6 +345,11 @@ M: invalid-slot-name summary
         [ >r tuple parse-tuple-slots r> prefix ]
     } case 3dup check-slot-shadowing ;
 
+ERROR: not-in-a-method-error ;
+
+M: not-in-a-method-error summary
+    drop "call-next-method can only be called in a method definition" ;
+
 ERROR: staging-violation word ;
 
 M: staging-violation summary

core/syntax/syntax.factor

@@ -189,8 +189,12 @@ IN: bootstrap.syntax
     ] define-syntax
 
     "call-next-method" [
-        current-class get literalize parsed
-        current-generic get literalize parsed
-        \ (call-next-method) parsed
+        current-class get current-generic get
+        2dup [ word? ] both? [
+            [ literalize parsed ] bi@
+            \ (call-next-method) parsed
+        ] [
+            not-in-a-method-error
+        ] if
     ] define-syntax
 ] with-compilation-unit