Interface for extracting xyShape.

[NunoSempere]

I want to be able to manipulate xyShapes, in order to do certain types of computations (see here).

One naïve way of doing this would be to have:

PointSet.toXYShape: (pointSetDist) => list<{x: number, y: number}>

However, Ozzie points out that pointsets could be Continuous, Discrete, or mixed.

Given this, we could have

A general interface

Which could look like:

PointSet.toXYShape: (pointSetDist) => {
  type: "Continuous"  | "Discrete" | "Mixed",
  continousXYShape?: list<{x: number, y: number}>,
  discreteXYShape?: list<{x: number, y: number}>,
}

or like

PointSet.toXYShape: (pointSetDist) => {
  type: "Continuous"  | "Discrete" | "Mixed",
  continousXYShape: list<{x: number, y: number}> | [],
  discreteXYShape: list<{x: number, y: number}> | [],
}

I think I prefer the second option because checking for the existence of an object property within Squiggle might be annoying, but checking if a list is empty would be easier.

An interface for each pointSet type

For continuous:

PointSet.continuousToXYShape: (continuousPointSetDist) => list<{x: number, y: number}>

For discrete:

PointSet.discreteToXYShape: (discretePointSetDist) => list<{x: number, y: number}>

For mixed:

PointSet.toXYShape: (mixedPointSetDist) => {
  continousXYShape: list<{x: number, y: number}>,
  discreteXYShape: list<{x: number, y: number}>,
}

---

One problem with this second option is that fragmenting this would make it more difficult to write general functions that manipulate any kind of pointSetDist. Overall I feel more partial about the first option.

[OAGr]

Kudos for writing this up so specifically. This proposal seems pretty reasonable to me and doesn't seem to be missing anything (that to me) is obvious.

[OAGr]

One potential issue is that we might want to call it something like toDict instead of toXYShape. We don't really have a native type for XYShape, so I'm not sure if it makes much sense to reference it publicly.

[OAGr]

I think mapX() could help here, but there are tricky edge cases to consider. #973