5 ms·

Without side effects you couldn't do anything. Pure functional languages make side effects explicit, but it isn't about them being missing.

by Sssnake 13y ago

nbouscal 13y ago
> Without side effects you couldn't do anything. Not true. > Pure functional languages make side effects explicit, but it isn't about them being missing. True. I should have been more clear about that.
- mturmon 13y ago
  Not a downvoter, but I believe "Without side effects you couldn't do anything" means that any interesting program ultimately has a side effect. The rocket is launched, the form is printed, pi is displayed on the monitor, etc.
  - kazagistar 13y ago
    Isn't that an effect, not neccesarily a side effect?
    - mturmon 13y ago
      "Function with side effect" is a term of art in functional programming. It's a function which (like all other functions) takes in arguments and puts out arguments (that's the "effect", if you like). But also, with a "side effect" -- the simplest example being, display something on the monitor. I.e., (display "hello world") returns whatever it returns (we throw it away), but also puts that string on the monitor. The latter action is not just computing a function (in the sense of FP) of the inputs. For more, see http://www.eecs.berkeley.edu/~bh/ssch20/io.html http://www.eecs.berkeley.edu/~bh/ssch20/io.html (search for "side effect").
- Sssnake 13y ago
  Yes true. Running a program with no side effects is a no-op. All side effect free programs are identical, and do nothing. This is one of the most common misconceptions people afraid to learn haskell bring up, because people keep saying "functional programming is having no side effects".
  - pera 13y ago
    It's funny: "not having side effects" was the main reason for me to start learning Haskell just because that idea didn't make much sense hah
  - nbouscal 13y ago
    So you're saying that a library that has no side effects but performs a complicated data transformation "doesn't do anything"?
    - Sssnake 13y ago
      A library is not a program.
      - nbouscal 13y ago
        Your claim was "Without side effects you couldn't do anything." I was rebutting that claim. Again, unless you want to claim that libraries "don't do anything." The more specific claim that you need side effects for a program to do anything is also false. You can prove mathematical theorems with programs that have no side effects. Of course now you'll say that that only works because of the compiler, which does have side effects, but that's really just moving the target so you can be "right" (as you did with this post). Even if theorem proving isn't good enough, since the entire purpose for having the term "side effects" is to be able to usefully discuss referential transparency, the other poster who noted that IO can be an effect and not necessarily a side effect was correct. If IO is isolated, it is not a side effect, it is just an effect. A good example of this is the execution of the main action in a Haskell program.
        13y ago

Without side effects you couldn't do anything. Pure functional languages make side effects explicit, but it isn't about them being missing.

by Sssnake 13y ago

Without side effects you couldn't do anything. Pure functional languages make side effects explicit, but it isn't about them being missing.

nbouscal 13y ago

> Without side effects you couldn't do anything. Not true. > Pure functional languages make side effects explicit, but it isn't about them being missing. True. I should have been more clear about that.

mturmon 13y ago
Not a downvoter, but I believe "Without side effects you couldn't do anything" means that any interesting program ultimately has a side effect. The rocket is launched, the form is printed, pi is displayed on the monitor, etc.
- kazagistar 13y ago
  Isn't that an effect, not neccesarily a side effect?
  - mturmon 13y ago
    "Function with side effect" is a term of art in functional programming. It's a function which (like all other functions) takes in arguments and puts out arguments (that's the "effect", if you like). But also, with a "side effect" -- the simplest example being, display something on the monitor. I.e., (display "hello world") returns whatever it returns (we throw it away), but also puts that string on the monitor. The latter action is not just computing a function (in the sense of FP) of the inputs. For more, see http://www.eecs.berkeley.edu/~bh/ssch20/io.html http://www.eecs.berkeley.edu/~bh/ssch20/io.html (search for "side effect").
Sssnake 13y ago
Yes true. Running a program with no side effects is a no-op. All side effect free programs are identical, and do nothing. This is one of the most common misconceptions people afraid to learn haskell bring up, because people keep saying "functional programming is having no side effects".
- pera 13y ago
  It's funny: "not having side effects" was the main reason for me to start learning Haskell just because that idea didn't make much sense hah
- nbouscal 13y ago
  So you're saying that a library that has no side effects but performs a complicated data transformation "doesn't do anything"?
  - Sssnake 13y ago
    A library is not a program.
    - nbouscal 13y ago
      Your claim was "Without side effects you couldn't do anything." I was rebutting that claim. Again, unless you want to claim that libraries "don't do anything." The more specific claim that you need side effects for a program to do anything is also false. You can prove mathematical theorems with programs that have no side effects. Of course now you'll say that that only works because of the compiler, which does have side effects, but that's really just moving the target so you can be "right" (as you did with this post). Even if theorem proving isn't good enough, since the entire purpose for having the term "side effects" is to be able to usefully discuss referential transparency, the other poster who noted that IO can be an effect and not necessarily a side effect was correct. If IO is isolated, it is not a side effect, it is just an effect. A good example of this is the execution of the main action in a Haskell program.
      - 13y ago