[Haskell-beginners] Trouble with formatting, Real World Haskell example

[Steven Ashley]

Hi Robert,

The contents of the do block must be indented at-least as much as
mainWith on the previous line.

For instance:

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 "Usage: Interact inputFile
outputFile"
....................myFunction = id


The haskell wikibook has some more detailed information of
http://en.wikibooks.org/wiki/Haskell/Indentation

Regards,

--Steven

2008/11/23 Robert Kosara <rkosara at gmail.com>:
> I'm having some trouble getting the InteractWith example from Real World
> Haskell's Chapter 4 to compile. When I use spaces (like below), it says
> "Interact.hs:10:30: Empty 'do' construct." When I use tabs (4 spaces per
> tab), I get "Interact.hs:16:13: parse error on input `='." In either case, I
> don't see the problem. Any help would be greatly appreciated.
> I'm also confused about the formatting of the example in the book (page 72).
> The last line ("myFunction = id") seems to be indented between the where and
> the next line, why is that? Is that simply a layout problem? To me, it seems
> it should be on the same level as the where.
> Below is my program:
> -- Interact.hs, simple filter in Haskell
> 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 "Usage: Interact inputFile outputFile"
>         myFunction = id
>
> Regards,
> Robert
>
> _______________________________________________
> Beginners mailing list
> Beginners at haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>