Re: [Haskell-cafe] generating Maybe

On Wed, 7 Nov 2007, Tim Newsham wrote:

Data.Maybe has functions for processing Maybe's but nothing useful for creating maybe. I think the following would be a very useful addition, a guarded function:

guarded :: (a -> Bool) -> (a -> b) -> a -> Maybe b guarded p f x | p x = Just (f x) | otherwise = Nothing

such a function in the std libs would make functions like "unfoldr" more attractive -- uses of foldr nearly always encapsulate this notion.

This would be guarded p f x = toMaybe (p x) (f x) in terms of my beloved but already rejected 'toMaybe': http://www.haskell.org/pipermail/libraries/2004-July/002326.html