diff --git a/src/compiler/SimpleEditor/JSON.hs b/src/compiler/SimpleEditor/JSON.hs
index 8f607dc84..06586c5eb 100644
--- a/src/compiler/SimpleEditor/JSON.hs
+++ b/src/compiler/SimpleEditor/JSON.hs
@@ -9,14 +9,24 @@ instance JSON Grammar where
   showJSON (Grammar name extends abstract concretes) =
     makeObj ["basename".=name, "extends".=extends,
              "abstract".=abstract, "concretes".=concretes]
+  readJSON = error "Grammar.readJSON intentionally not defined"
 
 instance JSON Abstract where
   showJSON (Abstract startcat cats funs) =
     makeObj ["startcat".=startcat, "cats".=cats, "funs".=funs]
+  readJSON = error "Abstract.readJSON intentionally not defined"
 
-instance JSON Fun   where showJSON (Fun   name typ) = signature  name typ
-instance JSON Param where showJSON (Param name rhs) = definition name rhs
-instance JSON Oper  where showJSON (Oper  name rhs) = definition name rhs
+instance JSON Fun where 
+  showJSON (Fun   name typ) = signature  name typ
+  readJSON = error "Fun.readJSON intentionally not defined"
+
+instance JSON Param where 
+  showJSON (Param name rhs) = definition name rhs
+  readJSON = error "Param.readJSON intentionally not defined"
+
+instance JSON Oper where 
+  showJSON (Oper  name rhs) = definition name rhs
+  readJSON = error "Oper.readJSON intentionally not defined"
 
 signature  name typ = makeObj ["name".=name,"type".=typ]
 definition name rhs = makeObj ["name".=name,"rhs".=rhs]
@@ -26,12 +36,15 @@ instance JSON Concrete where
     makeObj ["langcode".=langcode, "opens".=opens,
               "params".=params, "opers".=opers,
              "lincats".=lincats, "lins".=lins]
+  readJSON = error "Concrete.readJSON intentionally not defined"
 
 instance JSON Lincat where
   showJSON (Lincat cat lintype) = makeObj ["cat".=cat, "type".=lintype]
+  readJSON = error "Lincat.readJSON intentionally not defined"
 
 instance JSON Lin where
   showJSON (Lin fun args lin) = makeObj ["fun".=fun, "args".=args, "lin".=lin]
+  readJSON = error "Lin.readJSON intentionally not defined"
 
 infix 1 .=
 name .= v = (name,showJSON v)