Proposal To Revise Implicit Parameters

Scala Improvement Process
138

After playing around with implied instances and reading all docs, I’m intrigued about this approach. I don’t have anything to add semantic wise at this point, I like its current principles. But, given that this change is mostly about syntax, I think it might be useful to mention I struggle to get used to the implied syntax.

Isn’t there a better keyword we could use to refer to the same concept? Possibly a keyword that bears no indirect relationship with implicit and that doesn’t read as an adjective?

The one that comes to mind is infer. Given that implicits is a way to infer terms, it seems appropriate to use that word instead and it being a verb means it reads like I’m telling the computer to do something.

Here’s how the code snippet in Implied Instances would look like with it:

trait Ord[T] {
  def compare(x: T, y: T): Int
  def (x: T) < (y: T) = compare(x, y) < 0
  def (x: T) > (y: T) = compare(x, y) > 0
}

infer IntOrd for Ord[Int] {
  def compare(x: Int, y: Int) =
    if (x < y) -1 else if (x > y) +1 else 0
}

infer ListOrd[T] given (ord: Ord[T]) for Ord[List[T]] {
  def compare(xs: List[T], ys: List[T]): Int = (xs, ys) match {
    case (Nil, Nil) => 0
    case (Nil, _) => -1
    case (_, Nil) => +1
    case (x :: xs1, y :: ys1) =>
      val fst = ord.compare(x, y)
      if (fst != 0) fst else xs1.compareTo(ys1)
  }
}

Advantages of using infer over implied:

  1. It’s a verb and it’s similar to def both syntax wise (it comes from the verb define) and semantics-wise (it defines an inferred term without looking like a straight value definition).
  2. It’s two characters shorter.
  3. it reads nicely followed by for and given.

Disadvantages

  1. It’s not clear what we should use to import an inferrable instance. I prefer either infer import or import infer but we could also go for import inferred. If you don’t like either, we can probably find another variation that fits the bill.

EDIT: I’ve just seen @Odomontois already proposed the same thing in passing but no one seems to have given feedback on the suggestion.

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