fewer warnings, notably in Naproche-SAD;

--- a/src/Tools/Haskell/Haskell.thy	Sat Jan 23 14:17:02 2021 +0100
+++ b/src/Tools/Haskell/Haskell.thy	Sat Jan 23 17:26:40 2021 +0100
@@ -67,7 +67,6 @@
   space_explode, split_lines, trim_line, clean_name)
 where
 
-import Data.Maybe
 import qualified Data.List as List
 import qualified Data.List.Split as Split
 import qualified Isabelle.Symbol as Symbol
@@ -181,7 +180,6 @@
   (print_bool, parse_bool, parse_nat, print_int, parse_int, print_real, parse_real)
 where
 
-import Data.Maybe
 import qualified Data.List as List
 import qualified Text.Read as Read
 
@@ -307,6 +305,8 @@
 See also \<^file>\<open>$ISABELLE_HOME/src/Pure/PIDE/markup.ML\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
+
 module Isabelle.Markup (
   T, empty, is_empty, properties,
 
@@ -759,7 +759,6 @@
 module Isabelle.File (setup, read, write, append) where
 
 import Prelude hiding (read)
-import System.IO (IO)
 import qualified System.IO as IO
 
 setup :: IO.Handle -> IO ()
@@ -791,11 +790,11 @@
 See also \<^file>\<open>$ISABELLE_HOME/src/Pure/PIDE/xml.ML\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
+
 module Isabelle.XML (Attributes, Body, Tree(..), wrap_elem, unwrap_elem, content_of)
 where
 
-import qualified Data.List as List
-
 import Isabelle.Library
 import qualified Isabelle.Properties as Properties
 import qualified Isabelle.Markup as Markup
@@ -874,6 +873,8 @@
 See also \<^file>\<open>$ISABELLE_HOME/src/Pure/PIDE/xml.ML\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
+
 module Isabelle.XML.Encode (
   A, T, V, P,
 
@@ -965,6 +966,8 @@
 See also \<^file>\<open>$ISABELLE_HOME/src/Pure/PIDE/xml.ML\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
+
 module Isabelle.XML.Decode (
   A, T, V, P,
 
@@ -974,8 +977,6 @@
 )
 where
 
-import Data.List ((!!))
-
 import Isabelle.Library
 import qualified Isabelle.Value as Value
 import qualified Isabelle.Properties as Properties
@@ -1078,6 +1079,8 @@
 See also \<^file>\<open>$ISABELLE_HOME/src/Pure/PIDE/yxml.ML\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-missing-signatures -fno-warn-incomplete-patterns #-}
+
 module Isabelle.YXML (charX, charY, strX, strY, detect, output_markup,
   buffer_body, buffer, string_of_body, string_of, parse_body, parse)
 where
@@ -1205,6 +1208,8 @@
 See also \<^file>\<open>$ISABELLE_HOME/src/Pure/General/pretty.ML\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-missing-signatures #-}
+
 module Isabelle.Pretty (
   T, symbolic, formatted, unformatted,
 
@@ -1416,7 +1421,6 @@
 where
 
 import Isabelle.Library
-import qualified Isabelle.XML as XML
 import Isabelle.XML.Encode
 import Isabelle.Term
 
@@ -1457,11 +1461,12 @@
 See also \<^file>\<open>$ISABELLE_HOME/src/Pure/term_xml.ML\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-incomplete-patterns #-}
+
 module Isabelle.Term_XML.Decode (indexname, sort, typ, typ_body, term)
 where
 
 import Isabelle.Library
-import qualified Isabelle.XML as XML
 import Isabelle.XML.Decode
 import Isabelle.Term
 
@@ -1514,7 +1519,6 @@
 where
 
 import Data.ByteString (ByteString)
-import qualified Data.ByteString
 import Data.UUID (UUID)
 import qualified Data.UUID as UUID
 import Data.UUID.V4 (nextRandom)
@@ -1564,6 +1568,8 @@
 and \<^file>\<open>$ISABELLE_HOME/src/Pure/PIDE/byte_message.scala\<close>.
 -}
 
+{-# OPTIONS_GHC -fno-warn-incomplete-patterns #-}
+
 module Isabelle.Byte_Message (
     write, write_line,
     read, read_block, trim_line, read_line,
@@ -1577,11 +1583,8 @@
 import Data.ByteString (ByteString)
 import qualified Data.ByteString as ByteString
 import qualified Data.ByteString.UTF8 as UTF8
-import Data.Word (Word8)
-
-import Control.Monad (when)
+
 import Network.Socket (Socket)
-import qualified Network.Socket as Socket
 import qualified Network.Socket.ByteString as ByteString
 
 import Isabelle.Library hiding (trim_line)
@@ -1739,7 +1742,6 @@
 where
 
 import Data.Unique
-import Data.Maybe
 import Data.IORef
 import System.IO.Unsafe
 
@@ -1747,7 +1749,6 @@
 import Control.Monad (when, forM_)
 import Data.Map.Strict (Map)
 import qualified Data.Map.Strict as Map
-import Control.Exception.Base (SomeException)
 import Control.Exception as Exception
 import Control.Concurrent (ThreadId)
 import qualified Control.Concurrent as Concurrent