5 ms·

No, a program without effects is useless. Side effects, i.e. some action done on the side while evaluating the program are not required. There are other ways to

No, a program without effects is useless. Side effects, i.e. some action done on the side while evaluating the program are not required. There are other ways to treat effects in programs, particularly as values.

emodendroket 5y ago
Unless you display them, save them, send them somewhere, etc, they’re useless. Therefore, a program without side effects is useless.
- carnitine 5y ago
  Effects, yes. Side effects are a particular form of effect. A pure functional language can compose an effectful value that is interpreted by a runtime, but no effect happens on the side as the program is evaluated.
  - emodendroket 5y ago
    That’s not really what side effects mean in programming: https://en.wikipedia.org/wiki/Side_effect_(computer_science) https://en.wikipedia.org/wiki/Side_effect_(computer_science) > In computer science, an operation, function or expression is said to have a side effect if it modifies some state variable value(s) outside its local environment, that is to say has an observable effect besides returning a value (the intended effect) to the invoker of the operation.
    - ratww 5y ago
      GP is correct. There are zero side-effects inside a pure program. All the side-effects happen outside it, in a "runtime" (a better name IMO is "imperative shell") that exists totally separate from the program. The main() function of a pure program executes completely and terminates before any side effect has a chance to happen. I put quotes around runtime because it's not a runtime like an interpreter in dynamic languages, or a library that you can call from inside your pure program. This runtime just calls your main() function, which return a complex value (it's a chain of lambdas, to spoil it) that is interpreted by this runtime or "imperative shell". I understand this sounds unintuitive and might seem very confusing, but this is what makes useful pure programs possible. These couple presentations show how this type of boundary between imperative and functional code works with simpler type of program [1]. The only difference is that Haskell's "imperative shell" is lower-level than the presenter's. It only deals with IO, etc, whereas the presenter's imperative shell also has some domain code. [1] https://www.destroyallsoftware.com/talks/boundaries https://www.destroyallsoftware.com/talks/boundaries / https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/catalog/funct...

emodendroket 5y ago

Unless you display them, save them, send them somewhere, etc, they’re useless. Therefore, a program without side effects is useless.

carnitine 5y ago
Effects, yes. Side effects are a particular form of effect. A pure functional language can compose an effectful value that is interpreted by a runtime, but no effect happens on the side as the program is evaluated.
- emodendroket 5y ago
  That’s not really what side effects mean in programming: https://en.wikipedia.org/wiki/Side_effect_(computer_science) https://en.wikipedia.org/wiki/Side_effect_(computer_science) > In computer science, an operation, function or expression is said to have a side effect if it modifies some state variable value(s) outside its local environment, that is to say has an observable effect besides returning a value (the intended effect) to the invoker of the operation.
  - ratww 5y ago
    GP is correct. There are zero side-effects inside a pure program. All the side-effects happen outside it, in a "runtime" (a better name IMO is "imperative shell") that exists totally separate from the program. The main() function of a pure program executes completely and terminates before any side effect has a chance to happen. I put quotes around runtime because it's not a runtime like an interpreter in dynamic languages, or a library that you can call from inside your pure program. This runtime just calls your main() function, which return a complex value (it's a chain of lambdas, to spoil it) that is interpreted by this runtime or "imperative shell". I understand this sounds unintuitive and might seem very confusing, but this is what makes useful pure programs possible. These couple presentations show how this type of boundary between imperative and functional code works with simpler type of program [1]. The only difference is that Haskell's "imperative shell" is lower-level than the presenter's. It only deals with IO, etc, whereas the presenter's imperative shell also has some domain code. [1] https://www.destroyallsoftware.com/talks/boundaries https://www.destroyallsoftware.com/talks/boundaries / https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/catalog/funct...