I hope the spacing is preserved by my email client; here's a formatting that compiles: 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 On Sat, Nov 22, 2008 at 9:53 PM, Robert Kosara wrote:

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

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On Sat, Nov 22, 2008 at 10:41 PM, Ed McCaffrey wrote:

On Sat, Nov 22, 2008 at 9:53 PM, Robert Kosara wrote:

...

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@haskell.org http://www.haskell.org/mailman/listinfo/beginners

On Sun, Nov 23, 2008 at 12:10 AM, Steven Ashley wrote:

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

main = mainWith myFunction ....where mainWith function = do ....................args <- getArgs

This is the reason that I format 'where' clauses like so: main = mainWith myFunction ....where ....mainWith f = do ........args <- getArgs etc. I think one more line of vertical space is worth all of the horizontal space you end up saving. Kurt