scala/scala

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Fabio Labella

@SystemFw

I agree :)

the question of whether this should be called DI or not is probably a separate conversation

Dominic Egger

@GrafBlutwurst

code that actually does anything is impure and evil :D

Martijn Hoekstra

@martijnhoekstra

fun fact: code doesn't actually do anything at all

Josh

@joshlemer

code doesn't do side effects, people do side effects

Martijn Hoekstra

@martijnhoekstra

CPUs may do stuff with code that a compiler generated from the code you wrote, but if that's "close enough" to the code doing things, then I'd argue pure effects in an IOApp runtime is "close enough" as well

PsyfireX

@PsyfireX

The CPU was just following orders.

vijendra singh

@viju0731_twitter

value current is not a member of object java.sql.SQLException

not found: value JDBCConnectionException

Getting this error any help

PsyfireX

@PsyfireX

Could you copy a larger code-snippet?

Harrison Houghton

@hrhino

also, that's Java...

Josh

@joshlemer

Also I feel like it's so easy to "sneak in" mutability, if that makes sense. For example:

Seq[(String, Int)](
  "x" -> 1,
  "y" -> 2,
  "z" -> 3,
  "x" -> 2
).foldLeft(Map.empty[String, Int])(_ + _)

In a sense, we're reassigning a value to "x" here, right?

Harrison Houghton

@hrhino

... no? not any more than using updated on a map

Josh

@joshlemer

If you kinda squint at it and pretend that each line is binding to a variable then it's as if we have invented var out of purely functional constructs

PsyfireX

@PsyfireX

I don't get it, how are you assigning anything to "x"

"x" isn't mutable, nor is "x".->(2)

Martijn Hoekstra

@martijnhoekstra

@joshlemer sure, if you consider a Map[String, Int] as the runtime of your programming environment, with the strings as identifiers, updating values in that map can be seen as mutating values pointed to by identifiers

Josh

@joshlemer

Exactly @martijnhoekstra gets it

Martijn Hoekstra

@martijnhoekstra

but that's not scala, that's the Map[String, Int] language

Josh

@joshlemer

so if you aren't careful, mutability can "foam up" from beneath you

or rather, emerge would be the verb

Fabio Labella

@SystemFw

mutability is not a problem, lack of referential transparency is

also, that Map is a common technique to implement environments for closures when doing e.g. an interpreter :)

Josh

@joshlemer

a more flushed out example

sealed trait AssignmentTo 
case class Constant(c: Int) extends AssignmentTo
case class Variable(varName: String) extends AssignmentTo


Seq[(String, AssignmentTo)](
  "x" -> Constant(1),
  "y" -> Constant(2),
  "z" -> Constant(3),

  "uhoh" -> Variable("x"),

  "x" -> Constant(1),

  "uhoh" -> Variable("x")

).foldLeft(Map.empty[String, Int]) { case (acc, (ident, assign)) =>
  val newValue = assign match { 
    case Constant(c) => c
    case Variable(varName) => acc(varName)
  }
  acc + ((ident, newValue))
}

Martijn Hoekstra

@martijnhoekstra

The mutability there is in the interpreted language of AssignmentTo, not in scala

Josh

@joshlemer

like, aside from throwing exceptions, this is as pure as it gets.Yet, it is starting to look a lot like imperative programming

PsyfireX

@PsyfireX

I don't see the mutability

It seems like you're trying to prove a point by starting with "squint very hard"

Amit Prasad

@amitprasad01_twitter

Hi Guys

anyone familiar here of scalamock

Josh

@joshlemer

here we've invented a little world/language/abstraction where identifier can be mutably updated using only purely functional constructs

Amit Prasad

@amitprasad01_twitter

need some urgent help

Josh

@joshlemer

"x" can be assigned values, it can be read and assigned to other values, updated. It's a var

Pierre Marais

@Deeds67

@joshlemer Do you see recursion as mutation then as well?

Josh

@joshlemer

I'm not saying I have any answers or rules, just pointing out that purity maybe is less black and white than it seems?

PsyfireX

@PsyfireX

No, that's not what's happening.

"if you squint really hard 98 + 1 = 100"

Josh

@joshlemer

Unless there's like really a rule for why this is not to be breaking referential transparency

PsyfireX

@PsyfireX

^ that is an incorrect statement relying on ignoring logic/facts in favor of fuzzy logic

Josh

@joshlemer

@PsyfireX I'd like to hear why this is wrong if you wouldn't mind elaborating

PsyfireX

@PsyfireX

What is being mutated in your example?

Josh

@joshlemer

@amitprasad01_twitter I'm not familiar but if you pose specific questions maybe someone will know

@PsyfireX the binding of "x" to 1

Martijn Hoekstra

@martijnhoekstra

@joshlemer I see your exmple, but what you did was show that you can interpret an impure language in a pure interpreter. Just because you can use pure programming to write an interpreter to interpret an impure program doesn't make the interpreter impure.

PsyfireX

@PsyfireX

The binding is never mutated

Josh

@joshlemer

@PsyfireX I apologize, the second appearance of "x" should be "x" -> Constant(12345)

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