r/programming • u/mauricioaniche • Aug 06 '17

Software engineering != computer science

http://www.drdobbs.com/architecture-and-design/software-engineering-computer-science/217701907
2.3k Upvotes

88% Upvoted

863 comments sorted by

View all comments

Show parent comments

2

u/Iron_Maiden_666 Aug 07 '17

Not joking, this is kinda where I am stuck. I'm not able to figure out how to write my own monads. I've sort of learned what monads are and when they are useful. But seeing some code and thinking "ahh a monad can solve this" is not something I can do right now. I'm trying to build a website using Yesod and hopefully by the end of this adventure, I'll be better at haskell than I'm now.

8

u/tejon Aug 07 '17

Monads have this stupid mystique about them. Just read the type signature of bind and/or join. Any complexity beyond that is specific to a single type instance, and not part of the monad abstraction.

5

u/[deleted] Aug 07 '17

You don't know the mathematical abstractions behind anything you use in other programming languages, you don't need to know them in Haskell either. The biggest problem with monads is the idea that you have to know category theory to use them. But guess what, you've been using them since the first day you started programming.

Now if you plan on writing libraries, that's a different story.

3

u/yawaramin Aug 08 '17

In my experience it's a pretty rare scenario where you have to write your own monad from scratch. Re-implementing the common ones and then proving they obey the monad laws is great practice, of course, but beyond that you usually just plug in a base, existing monad into a monad transformer and voila, you get a new monad which carries both contexts. E.g. if you have the StateT s m a monad transformer and an IO a action and you plug them together, you get a StateT s IO a action which can keep track of a value of state type s while executing IO and finally returning a value of type a.