Doubt regarding Types

[Karthik Kumar]

Hi Artie, 
  You are right . I had changed the code as follows - 

run          = do c <- getBoardSize
                  validateBoardSize c
  
-- Get the board size as input  
getBoardSize :: IO ( Int ) 
validateBoardSize   :: Int -> IO () 


  ... and follows. 

run function is the entry point. 

Cheers
Karthik. 

--- Artie Gold <artiegold at austin.rr.com> wrote:
> Hal Daume III wrote:
> > Hi,
> > 
> > On Mon, 3 Nov 2003, Karthik Kumar wrote:
> > 
> >>-- Convert a string to an integer.
> >>-- This works perfectly fine. 
> >>atoi          :: [Char] -> Int
> >>atoi (h : []) = if isDigit h then digitToInt h else 0
> >>atoi (h : t) =  if isDigit h then digitToInt h * ( 10 ^ length t) +
> >>atoi t else 0
> > 
> > 
> > you can use "read" for this.
> > 
> > 
> >>-- validateBoardSize
> >>-- To validate the board size
> >>validateBoardSize   :: Int -> Bool
> >>validateBoardSize d = (d == 9 || d == 13 || d == 19 ) 
> > 
> > 
> > this looks fine
> > 
> > 
> >>getBoardSize :: IO Bool 
> >>-- TODO : What could be the type of getBoardSize 
> >>getBoardSize  = do c <- getLine
> >>                   validateBoardSize ( atoi c ) 
> >>
> >>ERROR "test1.hs":21 - Type error in final generator
> >>*** Term           : validateBoardSize (atoi c)
> >>*** Type           : Bool
> >>*** Does not match : IO a
> > 
> > 
> > this is telling you something important.  it's saying that the
> final 
> > generator, "validateBoardSize (atoi c)" has type Bool, but it's
> expecting 
> > it to have type IO something.  You need to "lift" the pure Bool
> value into  
> > IO by saying return:
> > 
> > 
> >>getBoardSize = do
> >>   c <- getLine
> >>   return (validateBoardSize (read c))
> > 
> > 
> 
> Of course the board size is now lost and gone forever (and a 
> function called `getBoardSize' returning an IO Bool is, well, a 
> little counterintuitive). ;-)
> 
> To the OP: What does the top level code look like?[1] That should 
> guide the rest of the design.
> 
> HTH,
> --ag
> 
> [1] The question is rhetorical.
> -- 
> Artie Gold -- Austin, Texas
> Oh, for the good old days of regular old SPAM.
> 


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