RE: Compiler error using IO

4 Jan 2002

      ...
| while :: IO Bool -> IO () -> IO ()
|
| while test action = do res <- test
|                         if res  then do action
|                                         while test action
|                                 else return ()
Haskell uses "layout" to reduce the need for parentheses.  For your code to
parse, "if" should align with "res" vertically, as in:
... = do res <- test
         if res ...
The "layout" rules drive me nuts. You might prefer using parentheses and 
semicolons, as I do:

-- (not tested)
while :: IO Bool -> IO () -> IO ();
while test action = do 
     {
     res <- test;
     if res
      then do
          {
          action;
          while test action;
          }
      else return ();
     };
--

...and then you can put the whitespace wherever you want.

-- 
Ashley Yakeley, Seattle WA