Anonymous recursion

[raviqqe]

Problem

• Currently, every recursion (iteration, loops, etc.) needs to be named because it needs to be a top-level function.

Solution

• Add anonymous recursion syntax.
  • There are some examples found in other languages like Clojure and Scala.
• Downsides are:
  • We have two ways to do one thing.
  • It's not really saving anything in terms of lines of codes.
• Should we limit this construct's use cases to strict evaluation and keep list comprehension?

Examples

Map

• This is a kind of useless example as we can simply unwrap the for loop.

squareMany = \(xs [number]) [number] {
  for {
    if [x, ...xs] = xs {
      [number x() * x(), ...recur]
    } else {
      [number]
    }
  }
}

Reduce

sum = \(xs [number]) number {
  y = 0

  for {
    if [x, ...xs] = xs {
      y = y + x()
      recur
    } else {
      y
    }
  }
}

Filter

squareMany = \(xs [number]) [number] {
  for {
    if [x, ...xs] = xs {
      if x() > 42 {
        [number x(), ...recur]
      } else {
        recur
      }
    } else {
      [number]
    }
  }
}

Zip

zip = \(xs [number], ys [number]) [number] {
  for {
    if [x, ...xs] = xs {
      if [y, ...ys] = ys {
        [number x() + y(), ...recur]
      } else {
        [number]
      }
    } else {
      [number]
    }
  }
}

References

• loop | ClojureDocs
• for loops | Scala
• Functional loop #1353

[sammy-hughes]

Is the intent here that the standard function "recur" would refer to the current scope?

[raviqqe]

Yes! I just added a References section that contains other languages' examples.

[sammy-hughes]

I was set to request a reducer combinator, but that approach absolutely satisfies any use-case I can think of!