Why am I getting parse error on myFunction

Question

In the following code, I'm getting parse error on input `myFunction':

import System.Environment (getArgs)
interactWith function inputFile outputFile = do  
    input <- readFile inputFile writeFile outputFile (function input)
main = mainWith myFunction  
 where mainWith function = do         
        args <- getArgs          
        case args of            
            [input,output] -> interactWith function input output         
            _ -> putStrLn "error: exactly two arguments needed"
        -- replace "id" with the name of our function below       
        myFunction = id 

Answer 1

myFunction = id needs to line up with the other thing defined in the where clause.

main = mainWith myFunction  
 where mainWith function = do         
     ^  args <- getArgs          
     |  case args of            
     |      [input,output] -> interactWith function input output         
     |      _ -> putStrLn "error: exactly two arguments needed"
     | -- replace "id" with the name of our function below       
     | myFunction = id 
     | ^
     | |
     | here
     |
     not here

The same code with more indentation to make it clear:

import System.Environment (getArgs)
interactWith function inputFile outputFile = do  
    input <- readFile inputFile 
    -- I assume a line break belongs here 
    writeFile outputFile (function input)
main = mainWith myFunction  
    where mainWith function = do         
              args <- getArgs          
              case args of            
                  [input,output] -> interactWith function input output         
                  _ -> putStrLn "error: exactly two arguments needed"
          -- replace "id" with the name of our function below       
          myFunction = id