[Haskell-cafe] NewLines in string

[Serge D. Mechveliani]

People,

Here is a certain naive question about string setting in a Haskell
program.
I have the functions   
       parseProgram :: String -> Program
       apply        :: Program -> Term -> Term    -- interpreter,

and try to build the example modules for them as in the following 
example:

  ----------------------------------------------------------------
  module Main where
  program = parseProgram
            "
             isOrdered nil      -> true;
             isOrdered (X:nil)  -> true;
             isOrdered (X:Y:Ys) -> 
                              isOrd (X > Y) (isOrdered (Y:Ys));

             isOrd true  bo -> false;
             isOrd false bo -> bo   
            "
            
  main = let {data = ... :: Term;  res = apply program data}
         in
         putStr $ concat ["data =  ",  shows data "\n",
                          "res =  ",   shows res "\n"]
  ----------------------------------------------------------------       
 
-- that is set a string (an object program example), 
parse it to a program, apply this program and print the result.
But in reality, the above string must be set like this:

  (2)
          "\
          \ isOrdered nil      -> true;\
          \ isOrdered (X:nil)  -> true;\
          \ isOrdered (X:Y:Ys) -> \
          \                    isOrd (X > Y) (isOrdered (Y:Ys));\
          \\
          \   isOrd true  bo -> false;\
          \   isOrd false bo -> bo\
          \"

-- because otherwise Haskell treats the NewLine characters in the above 
string in an unneeded way.
But with (2), the program  Main  occurs hard to read.

One could try to improve this by using  readFile.  Form the file 

  data.txt --------------------------------
             isOrdered nil      -> true;
             isOrdered (X:nil)  -> true;
             isOrdered (X:Y:Ys) -> 
                              isOrd (X > Y) (isOrdered (Y:Ys));

             isOrd true  bo -> false;
             isOrd false bo -> bo   
  -----------------------------------------

and combine   readFile "data.txt",  the `do' construct,
              pearseProgram, apply,  putStr.

But this needs adding one more file, and this also changes the 
programming style in defining examples.

Now, what is the difference?
1. readFile  reads string from file, with treating NewLine as needed.
2. The Haskell compiler reads the expression 
            parseProgram
            "
             isOrdered nil > true;
             ...
            "
   from the input Haskell program with treating NewLine in the string 
   in a different way.
I wonder: how to remove most of backslashes in the program (2) ?

Thank you in advance for your comments.

-----------------
Serge Mechveliani
mechvel at botik.ru