src/Tools/Code/code_haskell.ML

     (* print modules *)
     val import_includes_ps =
       map (fn (name, _) => str ("import qualified " ^ name ^ ";")) includes;
     fun print_module_frame module_name ps =
       (module_name, Pretty.chunks2 (
-        str "{-# OPTIONS_GHC -fglasgow-exts #-}"
-        :: str ("module " ^ module_name ^ " where {")
+        str ("module " ^ module_name ^ " where {")
         :: ps
         @| str "}"
       ));
     fun print_module module_name (gr, imports) =
       let

           let
             val _ = File.check destination;
             val filepath = (Path.append destination o Path.ext "hs" o Path.explode o implode
               o separate "/" o Long_Name.explode) module_name;
             val _ = File.mkdir_leaf (Path.dir filepath);
-          in File.write filepath (format [] width content) end
+          in
+            (File.write filepath o format [] width o Pretty.chunks2)
+              [str "{-# OPTIONS_GHC -fglasgow-exts #-}", content]
+          end
       | write_module width NONE (_, content) = writeln (format [] width content);
   in
     Code_Target.serialization
       (fn width => fn destination => K () o map (write_module width destination))
       (fn present => fn width => rpair (fn _ => error "no deresolving")