That syntax suggests the first pair will be flipped, and the rest will just be as they were, i.e. more like flip_first
When the pattern `[Posn(x, y), ...]` matches a list of positions,
since `Posn(x, y)` is followed by `...` the `x` is bound to a sequence of first coordinates and `y` is bound to a sequence of second coordinates.
In the template the `Posn(y, x)` is followed by `...` so the same number of positions is produced as the common length of x and y.
Typical pattern matching like in Haskell or Prolog wouldn't do this.
It makes perfect sense if you're used to the pattern matching of Scheme and Racket syntax macros.
I guess so, though that might be counterproductive to the goals of Rhombus.
Re:Rhombus Language
by laszlokorte on Tuesday March 18, 2025 @02:57PM
(#43403387)
What would be the corresponding syntax for matching and flipping only the first Posn?
If I had to guess:
fun flip_all([Posn(x, y), rest]):
[Posn(y, x), rest]
Your version would expect a list of two elements, you use & to indicate that you're collecting the remainder of the list as in:
fun flip_all([Posn(x, y), & rest]):
fun
| flip_all([]): []
| flip_all([Posn(x, y), & rest]):
[Posn(y, x), & flip_all(rest)]
If you really want flip_first it'd be:
fun flip_first([Posn(x, y), & rest]):
[Posn(y, x), & rest]In Haskell:
flip_one Posn(a,b) = Posn(b,a)
flip_first p:ps = flip one : ps
flip_all ps = map flip ps
The `[Posn(x, y), ...]` is a pattern that matches a list of positions. The `[Posn(y, x), ...]` is a template that produces a list of positions.