Message as String synonym to indicate preprocessing

Message remains a type synonym for String, indicating application of message function.

Crypto/Enigma.hs

@@ -532,26 +532,24 @@ enigmaEncoding ec str =
         zipWith encode (enigmaMapping <$> cfgs) (message str) where cfgs = iterate step (step ec)
 
 
-
-
--- REV - Make 'Message' a class and require explicty use of (replacement) 'message'; see issue 12 <<<
 -- Message entry -------------------------------------------------------------
 
--- | A 'String', to which 'message' is applied by functions taking it as an argument.
+-- | A (<https://wiki.haskell.org/Type_synonym#synonym> for) 'String', indicating that 'message' will be applied
+--   to the corresponding argument.
 type Message = String
 
 -- | Convert a 'String' to valid Enigma machine input: replace any symbols for which there are standard Kriegsmarine
 --   substitutions, remove any remaining non-letter characters, and convert to uppercase. This function is applied
 --   automatically to 'Message' arguments for functions defined here.
-message :: String -> String
+message :: String -> Message
 message s = filter (`elem` letters) $ foldl1 fmap (uncurry replace <$> subs) $ toUpper <$> s
     where
         subs = [(" ",""),(".","X"),(",","Y"),("'","J"),(">","J"),("<","J"),("!","X"),
                 ("?","UD"),("-","YY"),(":","XX"),("(","KK"),(")","KK"),
                 ("1","YQ"),("2","YW"),("3","YE"),("4","YR"),("5","YT"),
                 ("6","YZ"),("7","YU"),("8","YI"),("9","YO"),("0","YP")]
 
--- REV - Possible future version in which 'Message' is at type (and caller is responsible for making Message).
+-- REV - Rejected (#12) alternate version in which 'Message' is at class (and caller is responsible for making Message).
 -- data Message = Message String deriving Show
 --
 -- message :: String -> Message

Crypto/Enigma/Display.hs

@@ -73,8 +73,10 @@ markedMapping Nothing e     = e
 
 -- Machine operation display =================================================
 
--- Preprocess a message and produce a configuration display for the starting configuration
--- and for each character of the message, using the provided configuration display function.
+-- Preprocess a string into a 'Message' (using 'message') and produce a configuration display for the
+-- starting configuration and for each character of the message, using the provided configuration display function.
+-- Note that while 'showEnigmaOperation' and 'showEnigmaOperationInternal' indicate a 'Message' argument, it is
+-- this function, which both call, that applies 'message'.
 showEnigmaOperation_ :: (EnigmaConfig -> Char -> String) -> EnigmaConfig -> Message -> String
 showEnigmaOperation_ df ec str = unlines $ zipWith df (iterate step ec) (' ':(message str))
 
@@ -188,7 +190,7 @@ showEnigmaConfigInternal ec ch =
 -- Operation display ---------------------------------------------------------
 
 -- | Show a summary of an Enigma machine configuration (see 'showEnigmaConfig')
---   and for each subsequent configuration as it processes each letter of a message. #showEnigmaOperationEG#
+--   and for each subsequent configuration as it processes each letter of a 'Message'. #showEnigmaOperationEG#
 --
 --   >>> putStr $ showEnigmaOperation (configEnigma "b-γ-V-VIII-II" "LFAP" "UX.MO.KZ.AY.EF.PL" "03.17.04.11") "KRIEG"
 --       OHNKJYSBTEDMLCARWPGIXZQUFV  LFAP  10 16 24 06
@@ -201,11 +203,11 @@ showEnigmaConfigInternal ec ch =
 --   Note that the first line of the display represents the initial configuration of the machine, but does not
 --   perform any encoding (as explained in 'step').
 --   Note also that the second line of this display is the same as one displayed in the example for 'showEnigmaConfig'.
-showEnigmaOperation :: EnigmaConfig -> String -> String
+showEnigmaOperation :: EnigmaConfig -> Message -> String
 showEnigmaOperation ec str = showEnigmaOperation_ showEnigmaConfig ec str
 
 -- | Show a schematic of an Enigma machine's internal configuration (see 'showEnigmaConfigInternal' for details)
---   and for each subsequent configuration as it processes each letter of a message.
+--   and for each subsequent configuration as it processes each letter of a 'Message'.
 --
 --   >>> putStr $ showEnigmaOperationInternal (configEnigma "b-γ-V-VIII-II" "LFAP" "UX.MO.KZ.AY.EF.PL" "03.17.04.11") "KR"
 --       ABCDEFGHIJKLMNOPQRSTUVWXYZ
@@ -253,7 +255,7 @@ showEnigmaOperation ec str = showEnigmaOperation_ showEnigmaConfig ec str
 --   Note that the first block of the display represents the initial configuration of the machine, but does not
 --   perform any encoding (as explained in 'step'). Note also that the second block of this display is the same
 --   as one displayed in the example for 'showEnigmaConfigInternal', where it is explained in more detail.
-showEnigmaOperationInternal :: EnigmaConfig -> String -> String
+showEnigmaOperationInternal :: EnigmaConfig -> Message -> String
 showEnigmaOperationInternal ec str = showEnigmaOperation_ showEnigmaConfigInternal ec str