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He means that there's no type syntax to assist with monad creation or usage which indicates a sort of incomplete understanding of the concept. As an example, a

He means that there's no type syntax to assist with monad creation or usage which indicates a sort of incomplete understanding of the concept. As an example, a maybe monad in python can be implemented by having a monadic function return either: ["Just", 1] ["Nothing", None] and the bind operator (>>=) would be: bind = lambda a, f: a if a[0] == "Nothing" else f(a[1]) You should also understand that a list itself can be a monad. Monads are just burritos where ANY abstraction/design pattern can be the wrapping, it does not need a haskell type system to wrap something. Albeit the type system in haskell does really help you grok the concept. Weirdly how someone chooses to implement a monadic value and the bind operator suffers from the same problem as what this article writer complains about in OOP design patterns. Both monads and design patterns really depend on previous understanding of a pattern, and a variation on how someone chooses to implement the bind operator or a design pattern can really throw off people. Here is an example of an alternative variation of the "Maybe" monad in python, for the return values: ["Only", 1], None And a variation on bind: bind = lambda a, f: f(a[1]) if a is not None else None

sandGorgon 9y ago
this is a super interesting reply - you kind of translated these monadic concepts to python. Is there a resource for this ? or good old intuition ?
- crimsonalucard 9y ago
  Nah no single resource, it took me a lot of time to understand monads, going over many resources. Just remember Absolutely ANY design pattern / data structure can be a monad as long as you can get an internal value out of that abstraction and define a bind operator to compose monads together. This rule tells it all: (>>=) :: m a -> (a -> m b) -> m b m is the abstraction wrapper and a is the internal thing that is wrapped. You can wrap it in a type string, a list. Even like a binary tree can be a monad. You can define the bind operator to do whatever you want, it just needs to follow the type signature above and be associative.
- crimsonalucard 9y ago
  Oh and nothing was translated. A monad is a general concept applicable to almost any language. Deep understanding of a monad is to understand it outside of the haskell ecosystem.
runeks 9y ago
> You should also understand that a list itself can be a monad. A list is not a monad — it’s just a container of values, ie. a functor. A monad is a data structure defines a computation in a specific context, and allows composing these in a sequential manner. For example, the Haskell IO monad is a computational context in which you can do input/output, and all of these IO operations are represented using a data structure of the type “IO <return_value>”. For example, the function “readLine” has the type “IO String”, and represents a computation that reads a line from standard input and returns it as a string. At runtime, evaluating this value will result in the runtime system asking the user for some input, and at compile-time this is represented as the string (that the user enters at runtime) inside the IO monad.
- tome 9y ago
  > A list is not a monad Huh? List is very much a monad.
  - runeks 9y ago
    You're completely right. I had no idea. But I can't make sense of the definition of >>= for the list in Haskell, which is: xs >>= f = [y | x <- xs, y <- f x] It seems to imply that I get a list in return when I do xs >>= f, but I need to do the following in order for it to work: [1,2,3] >>= return . (+1)
    - tome 9y ago
      Perhaps this might help (or perhaps not!) > [1,-2,3] >>= (\x -> replicate (abs x) x) [1,-2,-2,3,3,3]
    - crimsonalucard 9y ago
      You're probably use to Monads that wrap a single object, like the maybe monad. Monads can wrap multiple objects or anything. This is the case for a list.

sandGorgon 9y ago

this is a super interesting reply - you kind of translated these monadic concepts to python. Is there a resource for this ? or good old intuition ?

crimsonalucard 9y ago
Nah no single resource, it took me a lot of time to understand monads, going over many resources. Just remember Absolutely ANY design pattern / data structure can be a monad as long as you can get an internal value out of that abstraction and define a bind operator to compose monads together. This rule tells it all: (>>=) :: m a -> (a -> m b) -> m b m is the abstraction wrapper and a is the internal thing that is wrapped. You can wrap it in a type string, a list. Even like a binary tree can be a monad. You can define the bind operator to do whatever you want, it just needs to follow the type signature above and be associative.
crimsonalucard 9y ago
Oh and nothing was translated. A monad is a general concept applicable to almost any language. Deep understanding of a monad is to understand it outside of the haskell ecosystem.

runeks 9y ago

> You should also understand that a list itself can be a monad. A list is not a monad — it’s just a container of values, ie. a functor. A monad is a data structure defines a computation in a specific context, and allows composing these in a sequential manner. For example, the Haskell IO monad is a computational context in which you can do input/output, and all of these IO operations are represented using a data structure of the type “IO <return_value>”. For example, the function “readLine” has the type “IO String”, and represents a computation that reads a line from standard input and returns it as a string. At runtime, evaluating this value will result in the runtime system asking the user for some input, and at compile-time this is represented as the string (that the user enters at runtime) inside the IO monad.

tome 9y ago
> A list is not a monad Huh? List is very much a monad.
- runeks 9y ago
  You're completely right. I had no idea. But I can't make sense of the definition of >>= for the list in Haskell, which is: xs >>= f = [y | x <- xs, y <- f x] It seems to imply that I get a list in return when I do xs >>= f, but I need to do the following in order for it to work: [1,2,3] >>= return . (+1)
  - tome 9y ago
    Perhaps this might help (or perhaps not!) > [1,-2,3] >>= (\x -> replicate (abs x) x) [1,-2,-2,3,3,3]
  - crimsonalucard 9y ago
    You're probably use to Monads that wrap a single object, like the maybe monad. Monads can wrap multiple objects or anything. This is the case for a list.