4 ms·
I'm having a tough time trying to understand what you're proposing. First of all, in Haskell there's no real concept of having functions "attached" to objects (
by thinkpad20 11y ago
I'm having a tough time trying to understand what you're proposing. First of all, in Haskell there's no real concept of having functions "attached" to objects (in the OO sense). The closest analogue is a type class, which relates a type to a set of functions. For monad, that looks like
class Monad m where
return :: a -> m a
(>>=) :: m a -> (a -> m b) -> m b
And it's up to the particular instance to determine how those functions are implemented. For example,
instance Monad Maybe where
return :: a -> Maybe a
return x = Just x
(>>=) :: Maybe a -> (a -> Maybe b) -> Maybe b
maybe >>= f = case maybe of
Nothing -> Nothing
Just x -> f x
The definition of the State type, and its corresponding Monad instance, is a little more involved (I suggest this blog post for an explanation [1]):
newtype State s a = State { runState :: s -> (a, s) }
instance Monad (State a) where
return x = State $ \s -> (x, s)
m >>= k = State $ \s -> let (a, s') = runState m s
in runState (k a) s'
I'm honestly not quite sure what you mean by the rest of it (for example, "ignoring the function requirement", "specialness" etc). But the bottom line is that you can do any typesafe thing you want to, within the rules of how the language works.
[1]: http://brandon.si/code/the-state-monad-a-tutorial-for-the-confused/ http://brandon.si/code/the-state-monad-a-tutorial-for-the-co...
- sago 11y agoThanks again. Sorry, I wasn't talking about Haskell. Following the OP I was talking about the merits of using these concepts or structures in other languages (C++, as per the OP, in particular). Of course, in a language with strong support and syntax for a particular pattern, you should rely on that pattern. But beyond that, it can be useful to use a pattern in other languages. Carmack is talking about writing C++ in a more functional style. I've written OO plain C, for example, when that pattern has made sense, and much of my C++ is heavily influenced by my experience with Scheme. My point was that I don't get the emphasis on Monads, as a concept, for the range of things it gets emphasised for. In a language which has core syntactic and semantic support, and there are few alternatives, then of course it has to be used widely. But that's a different argument to saying it is an intrinsically good solution for those cases. I might be missing something, but as an architectural pattern in general it doesn't seem appealing. Not enough to reimplement in another language. That's the context to my comment on typesafety. You said that other languages aren't typesafe enough. I was suggesting that, implementing a monad as a structure or an object would be typesafe, so I couldn't see what was insufficient.