Fixpoint.hs

module Utility.Fixpoint (
    fix
  , fixUnbounded
  , fixMaybe
  ) where

--------------------------------------------------------------

fix :: (Show a, Eq a) => Int -> (a -> a) -> a -> a
fix (-1)     _ _ = error "fix: Exceeded maxIters"
fix maxIters f x = let x' = f x in
                   if x' == x then
                     x
                   else
                     fix (maxIters - 1) f x'

fixUnbounded :: (Eq a) => (a -> a) -> a -> a
fixUnbounded f x = let x' = f x in
                   if x' == x then
                     x
                   else
                     fixUnbounded f x'

fixMaybe :: (Eq a) => (a -> Maybe a) -> a -> Maybe a
fixMaybe f x = case f x of
                 Nothing -> Nothing
                 Just x' -> if x' == x then
                              Just x
                            else
                              fixMaybe f x'