0e671a1a ​

let p1: Loc
let p2: Loc
let p3: Loc
let g: Grid

let input = g
  |> point (p1.x, p1.y, red)
  |> point (p2.x, p2.y, yellow)
  |> point (p3.x, p3.y, green)

let output = g
  |> vline p1.x p2.x p1.y gray
  |> hline p2.x p1.y p2.y gray
  |> vline p2.x p3.x p2.y gray
  |> hline p3.x p2.y p3.y gray
  |> point (p1.x, p1.y, red)
  |> point (p2.x, p2.y, yellow)
  |> point (p3.x, p3.y, green)