Iavor wrote:
I propose that we add the following combinators to the 'Control.Applicative' module:
Here's a bunch, I've been using for quite some time now: infixl 5 <?>, <??>, <<?>, <?>> infixl 4 <$$>, <^>, <^, <^^>, , , <+> infixl 3 <||> infixl 2 `opt` (<$$>) :: (Applicative f) => f a -> (a -> b) -> f b v <$$> f = v <**> pure f (<^>) :: (Applicative f) => f (a -> b -> c) -> f b -> f (a -> c) l <^> r = flip <$> l <*> r (<^) :: (Applicative f) => f (a -> b -> c) -> f d -> f (b -> a -> c) l <^ r = flip <$> l <* r (<^^>) :: (Applicative f) => f b -> f (a -> b -> c) -> f (a -> c) l <^^> r = l <**> (flip <$> r) () :: (Applicative f) => (a -> b -> c) -> f b -> f (a -> c) f v = flip f <$> v ( (a -> b -> c) -> f d -> f (b -> a -> c) f ) :: (Applicative f) => f b -> (a -> b -> c) -> f (a -> c) v f = v <$$> flip f (<+>) :: (Applicative f) => f a -> f b -> f (a, b) l <+> r = (,) <$> l <*> r (<||>) :: (Alternative f) => f a -> f b -> f (Either a b) l <||> r = Left <$> l <|> Right <$> r (<?>) :: (Alternative f) => a -> f a -> f a x <?> v = v <|> pure x (<??>), opt :: (Alternative f) => f a -> a -> f a v <??> x = v <|> pure x opt = (<??>) (<<?>) :: (Alternative f) => f (a -> a) -> f a -> f a l <<?> r = id <?> l <*> r (<?>>) :: (Alternative f) => f a -> f (a -> a) -> f a l <?>> r = l <**> r <??> id packed :: (Applicative f) => f a -> f b -> f c -> f c packed l r v = l *> v <* r choice :: (Alternative f) => [f a] -> f a choice = foldr (<|>) empty foldrMany :: (Alternative f) => (a -> b -> b) -> b -> f a -> f b foldrMany op e v = go where go = op <$> v <*> go `opt` e foldrSome :: (Alternative f) => (a -> b -> b) -> b -> f a -> f b foldrSome op e v = op <$> v <*> go where go = op <$> v <*> go `opt` e foldlMany :: (Alternative f) => (b -> a -> b) -> b -> f a -> f b foldlMany op e v = go <*> pure e where go = op <!> v <!!> (.) <*> go `opt` id foldlSome :: (Alternative f) => (b -> a -> b) -> b -> f a -> f b foldlSome op e v = op e <$> v <**> go where go = op <!> v <!!> (.) <*> go `opt` id foldrSepMany :: (Alternative f) => (a -> b -> b) -> b -> f c -> f a -> f b foldrSepMany op e u v = op <$> v <*> go `opt` e where go = op <$ u <*> v <*> go `opt` e foldrSepSome :: (Alternative f) => (a -> b -> b) -> b -> f c -> f a -> f b foldrSepSome op e u v = op <$> v <*> go where go = op <$ u <*> v <*> go `opt` e foldlSepMany :: (Alternative f) => (b -> a -> b) -> b -> f c -> f a -> f b foldlSepMany op e u v = op e <$> v <**> go `opt` e where go = op <! u <*> v <!!> (.) <*> go `opt` id foldlSepSome :: (Alternative f) => (b -> a -> b) -> b -> f c -> f a -> f b foldlSepSome op e u v = op e <$> v <**> go where go = op <! u <*> v <!!> (.) <*> go `opt` id sepMany, sepSome :: (Alternative f) => f b -> f a -> f [a] sepMany = foldrSepMany (:) [] sepSome = foldrSepSome (:) [] chainr :: (Alternative f) => f (a -> a -> a) -> f a -> f a chainr u v = v <?>> go where go = u <^> v > go chainl :: (Alternative f) => f (a -> a -> a) -> f a -> f a chainl u v = v <**> go where go = (.) (u <^> v) <*> go `opt` id Cheers, Stefan