3 ms·

"flatmap" hints at it consisting of two components, flattening and mapping. Both are to be seen in a generalized context though, and the words are familiar to m

by quchen 11y ago

"flatmap" hints at it consisting of two components, flattening and mapping. Both are to be seen in a generalized context though, and the words are familiar to many when thinking about collections. 1. Mapping - the same as what Functor/Mappable provides. We use this to "map" over a structure, producing a nested structure. 2. Flattening: we just built our nested structure, time to squash it again. In types akin to templates, Structure<A> ------------------------ (map something suitable over it) Structure<Structure<B>> ------------------------ (flatten it) Structure<B> It's not a terrible name, but it probably doesn't help seeing the bigger picture either. "Flattening" a parser, a subroutine, an empty thing -- that's not really something very intuitive.

Tyr42 11y ago
Join (flatten) is a fundamental monadic operation. join:: m (m a) -> m a I have a parser of a single character and a way to generate new character parsers char :: Char -> Parser Char x :: (Parser Char) let y = fmap (char . toUpper) x :: (Parser (Parser Char)) It's a parser which creates a new parser out of the input it consumes. I do think that fmap/pure/join is the easier to understand set of defining functions for monads.
- quchen 11y ago
  join is one possible fundamental monadic operation. You can also define monads in other ways, such as endofunctors such that the Kleisli structure forms a category. In this case, you have the identity arrow (called return in Haskell) and Kleisli composition (<=< in Haskell) as fundamental operations. Neither of these is more fundamental than the other. You can convert back and forth, f >=> g = \x -> f x >>= g m >>= f = (f <=< id) m join = (>>= id) m >>= f = join (fmap f m) So if you're focused on composing monadic operations, thinking about it in terms of >=> is often a good idea.

by quchen 11y ago

Tyr42 11y ago

Join (flatten) is a fundamental monadic operation. join:: m (m a) -> m a I have a parser of a single character and a way to generate new character parsers char :: Char -> Parser Char x :: (Parser Char) let y = fmap (char . toUpper) x :: (Parser (Parser Char)) It's a parser which creates a new parser out of the input it consumes. I do think that fmap/pure/join is the easier to understand set of defining functions for monads.

quchen 11y ago
join is one possible fundamental monadic operation. You can also define monads in other ways, such as endofunctors such that the Kleisli structure forms a category. In this case, you have the identity arrow (called return in Haskell) and Kleisli composition (<=< in Haskell) as fundamental operations. Neither of these is more fundamental than the other. You can convert back and forth, f >=> g = \x -> f x >>= g m >>= f = (f <=< id) m join = (>>= id) m >>= f = join (fmap f m) So if you're focused on composing monadic operations, thinking about it in terms of >=> is often a good idea.