[Haskell-cafe] separate input calculation output

Robert Vollmert rvollmert-lists at gmx.net
Tue Mar 25 05:36:49 EDT 2008

On Mar 25, 2008, at 09:13, Thomas Engel wrote:
> My problem is: How can I get the input values into the calculations  
> and back
> the result to the output.
> In an other language I would use global variables for this. So what  
> should I
> use in haskell?

(I think I know enough haskell to answer this, but I may be telling  
you all the wrong things.)

You'll have to pass the values through, though this can be hidden to  
some extent. Try changing your functions to have types

type Input = (Float, Float, ...)
type Output = (Float, Float, ...)

inputvalues :: IO Input     -- add a "return (ve,de,...)" to the end
compute :: Input -> Output
outputvalues :: Output -> IO ()

You could then wrap them in

main :: IO ()
main = do input <- inputvalues
           outputvalues (compute input)

This should do what you want.

It might be improved upon by using data types with appropriately named  
fields instead of tuples so as to keep your variable names around.


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