eftCharFB :: (Char -> a -> a) -> a -> Int# -> Int# -> a
eftCharFB c n x0 y = go x0
                 where
                    go x | isTrue# (x ># y) = n
                         | otherwise        = C# (chr# x) `c` go (x +# 1#)


eftCharFB :: (Char -> a -> a) -> a -> Int# -> Int# -> a
eftCharFB c n x0 y = go x0
                 where
                    go x | isTrue# (x ># y) = n
                         | otherwise        = C# (chr# x) `c` go (x +# 1#)


eftCharFB c n x0 y = go x0
                 where
                    go x | isTrue# (x ># y) = n
                         | otherwise        = C# (chr# x) `c` go (x +# 1#)

