4 ms·

Where do I have to 'understand "Monad"' to write this? main = do x <- readLn y <- readLn print (x + y) Do I have to 'understand "Monad"'

by tome 3y ago

Where do I have to 'understand "Monad"' to write this? main = do x <- readLn y <- readLn print (x + y) Do I have to 'understand "Monad"' to write this? def main(): x = input() y = input() print(x + y)

lmm 3y ago
> Where do I have to 'understand "Monad"' to write this? The recommended explanation of what <- is/does will be about "Monad".
- tome 3y ago
  You're moving the goalposts! You said 'the recommended way of writing a program to e.g. read two numbers from the user, add them, and print the result, demands understanding "Monad".'
  - Tainnor 3y ago
    I don't think it's "moving the goalposts" when you demand that you can understand, at least to a first-order approximation, what the code that you write is doing. Yes, you could just treat IO as a black box and memorize a bunch of weird syntax rules, but you're going to have a hard time very quickly, especially when you change something and the compiler throws errors at you. FWIW, I think that monads are a powerful abstraction, but they're certainly not incredibly natural and Haskell basically just throws them at you from day 1.
  - lmm 3y ago
    The recommended way of writing a program in most languages demands some level of understanding what you're writing. You would have to somehow come up with the "<-" parts of that program, and the recommended way of doing that is to understand Monad.
    - tome 3y ago
      > The recommended way of writing a program in most languages demands some level of understanding what you're writing Sure, some. I think this discussion is about exactly what and how much, when it comes to Haskell. > the recommended way of doing that is to understand Monad. That doesn't ring true to me, not from how I learned Haskell and not by analogy with how I learned other languages. I don't remember having to "understand Monad" to write in "do" notation. Quite the opposite in fact. I vividly remember trying to "understand Monad" and being unable to, and then just giving up and trying to use do notation, finding it easy, completely unhelped by what I was trying to "understand", and regretting having spent all the time "understanding". But it's been a long time since I learned a language so maybe I'm mistaken. I would appreciate the point of view of others who have fresher eyes. I will concede that people have a harder time learning Haskell than Python (although I don't think anyone understands the exact reasons) but you gave a very specific example of a program that is supposedly requires some deep understanding to write in Haskell. I wanted to give a counterpoint so people can decide for themselves. That's as far as my claim goes.
itishappy 3y ago
> Where do I have to 'understand "Monad"' to write this? Literally every line? Your example makes it seem so simple! "Do" for function declarations, "<-" for variable assignment... Haskell is just like python! Alright, here I go! fact n = do n' <- n - 1 if n <= 1 then 1 else n * fact n' Uh oh... Couldn't match type `t' with `m t' Expected: t -> m t Actual: m t -> m t What the heck is "m t"?
- bPspGiJT8Y 3y ago
  fact n = do let n' = n - 1 if n <= 1 then 1 else n * fact n' Here you go. Not sure about Haskell but in PureScript it compiles. Use "<-" for functions which return a value in IO type constructor, otherwise use "let".
  - deleted 3y ago
    [deleted]
  - itishappy 3y ago
    That's kinda the point though, right? There's something different about this `IO` thing that uses special syntax. You might be able to guess something and get it to compile, but should you? fact n = do let n' = do n - 1 if do n <= 1 then do 1 else do n * fact n'
- tome 3y ago
  > What the heck is "m t"? It's worse than that! What the heck is "->"? But I don't particularly buy the argument. Alright, here I go: def main(): x = input y = input print(x + y) Uh oh... Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'builtin_function_or_method' and 'builtin_function_or_method' What the heck is "Traceback", "<stdin>", "<module>", "TypeError", "operand", "builtin_function_or_method"? Did I have to understand all those to write the simple Python program? The claim that you have to understand everything about a failure case in order to write simple programs doesn't seem valid to me. It doesn't resonate with how I've learned languages before. However, I may not have the best perspective because I'm very familiar with both Python and Haskell so I don't have the "beginners mind" any more. I would be interested to hear from someone who's a beginner (perhaps in both languages) whether they think the Haskell program requires more understanding than the Python one https://news.ycombinator.com/item?id=37402253 https://news.ycombinator.com/item?id=37402253

by tome 3y ago

lmm 3y ago

> Where do I have to 'understand "Monad"' to write this? The recommended explanation of what <- is/does will be about "Monad".

tome 3y ago
You're moving the goalposts! You said 'the recommended way of writing a program to e.g. read two numbers from the user, add them, and print the result, demands understanding "Monad".'
- Tainnor 3y ago
  I don't think it's "moving the goalposts" when you demand that you can understand, at least to a first-order approximation, what the code that you write is doing. Yes, you could just treat IO as a black box and memorize a bunch of weird syntax rules, but you're going to have a hard time very quickly, especially when you change something and the compiler throws errors at you. FWIW, I think that monads are a powerful abstraction, but they're certainly not incredibly natural and Haskell basically just throws them at you from day 1.
- lmm 3y ago
  The recommended way of writing a program in most languages demands some level of understanding what you're writing. You would have to somehow come up with the "<-" parts of that program, and the recommended way of doing that is to understand Monad.
  - tome 3y ago
    > The recommended way of writing a program in most languages demands some level of understanding what you're writing Sure, some. I think this discussion is about exactly what and how much, when it comes to Haskell. > the recommended way of doing that is to understand Monad. That doesn't ring true to me, not from how I learned Haskell and not by analogy with how I learned other languages. I don't remember having to "understand Monad" to write in "do" notation. Quite the opposite in fact. I vividly remember trying to "understand Monad" and being unable to, and then just giving up and trying to use do notation, finding it easy, completely unhelped by what I was trying to "understand", and regretting having spent all the time "understanding". But it's been a long time since I learned a language so maybe I'm mistaken. I would appreciate the point of view of others who have fresher eyes. I will concede that people have a harder time learning Haskell than Python (although I don't think anyone understands the exact reasons) but you gave a very specific example of a program that is supposedly requires some deep understanding to write in Haskell. I wanted to give a counterpoint so people can decide for themselves. That's as far as my claim goes.

itishappy 3y ago

> Where do I have to 'understand "Monad"' to write this? Literally every line? Your example makes it seem so simple! "Do" for function declarations, "<-" for variable assignment... Haskell is just like python! Alright, here I go! fact n = do n' <- n - 1 if n <= 1 then 1 else n * fact n' Uh oh... Couldn't match type `t' with `m t' Expected: t -> m t Actual: m t -> m t What the heck is "m t"?

bPspGiJT8Y 3y ago
fact n = do let n' = n - 1 if n <= 1 then 1 else n * fact n' Here you go. Not sure about Haskell but in PureScript it compiles. Use "<-" for functions which return a value in IO type constructor, otherwise use "let".
- deleted 3y ago
  [deleted]
- itishappy 3y ago
  That's kinda the point though, right? There's something different about this `IO` thing that uses special syntax. You might be able to guess something and get it to compile, but should you? fact n = do let n' = do n - 1 if do n <= 1 then do 1 else do n * fact n'
tome 3y ago
> What the heck is "m t"? It's worse than that! What the heck is "->"? But I don't particularly buy the argument. Alright, here I go: def main(): x = input y = input print(x + y) Uh oh... Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for +: 'builtin_function_or_method' and 'builtin_function_or_method' What the heck is "Traceback", "<stdin>", "<module>", "TypeError", "operand", "builtin_function_or_method"? Did I have to understand all those to write the simple Python program? The claim that you have to understand everything about a failure case in order to write simple programs doesn't seem valid to me. It doesn't resonate with how I've learned languages before. However, I may not have the best perspective because I'm very familiar with both Python and Haskell so I don't have the "beginners mind" any more. I would be interested to hear from someone who's a beginner (perhaps in both languages) whether they think the Haskell program requires more understanding than the Python one https://news.ycombinator.com/item?id=37402253 https://news.ycombinator.com/item?id=37402253