Clojure is not statically typed, so doesn’t need the strict this/that/whatever type declarations that are necessary in haskell (and, I gather, Scala). If you want to return a string, you return a string; if you return nil instead, that’s okay too. “Functional” does not correspond exactly to “strict compile-time typing”. They are orthogonal concepts, and … Read more
I don’t use ST much, but sometimes it is just the best solution. This can be in many scenarios: There are already well-known, efficient ways to solve a problem. Quicksort is a perfect example of this. It is known for its speed and in-place behavior, which cannot be imitated by pure code very well. You … Read more
UDATE. See this new library providing functor and monad operators for plain callback-based functions that do not have the issues with theneables: https://github.com/dmitriz/cpsfy The JS Promise is neither a Functor nor an Applicative nor a Monad It is not a functor, because the composition preservation law (sending compositions of functions to compositions of their images) … Read more
do notation in Haskell desugars in a pretty simple way. do x <- foo e1 e2 … turns into foo >>= \x -> do e1 e2 and do x e1 e2 … into x >> do e1 e2 …. This means you can really write any monadic computation with >>= and return. The only reason … Read more
A monad only supplies two functions: return :: Monad m => a -> m a (>>=) :: Monad m => m a -> (a -> m b) -> m b Both of these return something of type m a, so there is no way to combine these in any way to get a function of … Read more
The point is so there can be clean error handling in a chain of functions, containers, and side effects. Is this a correct interpretation? Not really. You’ve mentioned a lot of concepts that people cite when trying to explain monads, including side effects, error handling and non-determinism, but it sounds like you’ve gotten the incorrect … Read more
This probably isn’t the answer you’re looking for, but here you go anyways: A really crooked way of looking at monads & co. One way of looking at abstract concepts like these is to link them with basic concepts, such as ordinary list processing operations. Then, you could say that, A category generalizes the (.) … Read more
Phil Wadler has written many papers on monads, but the one to read first is a lot of fun and will be accessible to any programmer; it’s called The essence of functional programming. The paper includes source code and sample usages. A personal favorite of mine is the probability monad; if you can find Sungwoo … Read more
This question has some good answers: Monads as adjunctions More to the point, Derek Elkins’ “Calculating Monads with Category Theory” article in TMR #13 should have the sort of constructions you’re looking for: http://www.haskell.org/wikiupload/8/85/TMR-Issue13.pdf Finally, and perhaps this is really the closest to what you’re looking for, you can go straight to the source and … Read more
For all the standard mtl monads, you don’t need lift at all. get, put, ask, tell — they all work in any monad with the right transformer somewhere in the stack. The missing piece is IO, and even there liftIO lifts an arbitrary IO action down an arbitrary number of layers. This is done with … Read more