Secant.hs

#!/usr/bin/env runhaskell

ε = 1.0e-7

-- sqrt(7)
f x = x * x - 7

-- secant :: (a -> a) -> a -> a -> a
secant f x = secant' f xLast x
    where xLast = x - 0.01
          secant' f xLast x | abs (xNext - x) <= ε = xNext
                           | otherwise            = secant' f x xNext
          xNext = x - (f x) * (xLast - x) / ((f xLast) - (f x))      
    
    --if abs (xNext - x) <= ε 
--    then xNext
  --  else secant f x  xNext
--    where 

main = do
    let fx = secant f 2.0
    putStrLn ("Roots of sqrt(7) are " ++ (show fx))