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I completely agree. Just write pure functions as much as possible and you're good. What goes inside a function doesn't matter so long as the function itself is

by mrloba 6y ago

I completely agree. Just write pure functions as much as possible and you're good. What goes inside a function doesn't matter so long as the function itself is pure, imo

mrkeen 6y ago
Do you have any examples of compilers or linters that assist with this? Any kind of error or warning would do.
- tome 6y ago
  Haskell has ST[1], which allows you to do mutable in place updates in a way that the compiler can guarantee are not visible from the outside. It's not particularly popular though. Typically it seems to be more convenient to either be thoroughly pure or accept mutability and use IO. [1] https://hackage.haskell.org/package/base-4.14.0.0/docs/Control-Monad-ST.html https://hackage.haskell.org/package/base-4.14.0.0/docs/Contr...
  - jacinabox 6y ago
    There's also the probably underappreciated packages ref-tf and ref-fd which let you write code that is polymorphic over the type of state reference. These can make 'ST' more acceptable because you don't have to make the decision of what state reference to use up front.
- mrloba 6y ago
  Not really unfortunately. In typescript/javascript you have a few options, but none that are any good. In js you can freeze an object to avoid mutation, but there's a performance penalty and a lot of hassle. As for side effects, you have the async keyword which often tells you if a function contains a side effect or not. In typescript you can use readonly for objects and arrays to avoid mutation, but it becomes a hassle for nested objects, and it doesn't work for local state where it's actually ok to mutate things. There is an issue open for typescript that proposes to add a "pure" keyword, but I think it's quite hard to implement. What I do instead these days is to separate pure from impure by using separate files, but as you noted in a sibling comment, this can quickly fall apart if people aren't onboard with the idea.

by mrloba 6y ago

I completely agree. Just write pure functions as much as possible and you're good. What goes inside a function doesn't matter so long as the function itself is pure, imo

mrkeen 6y ago

Do you have any examples of compilers or linters that assist with this? Any kind of error or warning would do.

tome 6y ago
Haskell has ST[1], which allows you to do mutable in place updates in a way that the compiler can guarantee are not visible from the outside. It's not particularly popular though. Typically it seems to be more convenient to either be thoroughly pure or accept mutability and use IO. [1] https://hackage.haskell.org/package/base-4.14.0.0/docs/Control-Monad-ST.html https://hackage.haskell.org/package/base-4.14.0.0/docs/Contr...
- jacinabox 6y ago
  There's also the probably underappreciated packages ref-tf and ref-fd which let you write code that is polymorphic over the type of state reference. These can make 'ST' more acceptable because you don't have to make the decision of what state reference to use up front.
mrloba 6y ago
Not really unfortunately. In typescript/javascript you have a few options, but none that are any good. In js you can freeze an object to avoid mutation, but there's a performance penalty and a lot of hassle. As for side effects, you have the async keyword which often tells you if a function contains a side effect or not. In typescript you can use readonly for objects and arrays to avoid mutation, but it becomes a hassle for nested objects, and it doesn't work for local state where it's actually ok to mutate things. There is an issue open for typescript that proposes to add a "pure" keyword, but I think it's quite hard to implement. What I do instead these days is to separate pure from impure by using separate files, but as you noted in a sibling comment, this can quickly fall apart if people aren't onboard with the idea.