3 ms·

That syntax suggests the first pair will be flipped, and the rest will just be as they were, i.e. more like flip_first

by arunix 2y ago

soegaard 2y ago
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.
- Y_Y 2y ago
  Typical pattern matching like in Haskell or Prolog wouldn't do this.
  - shawn_w 2y ago
    It makes perfect sense if you're used to the pattern matching of Scheme and Racket syntax macros.
    - Y_Y 2y ago
      I guess so, though that might be counterproductive to the goals of Rhombus.
- laszlokorte 2y ago
  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] If I am correct then the only difference between flipping all and flipping just the first is `...` vs `rest`
  - Jtsummers 2y ago
    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]): You'd need to amend the logic of the function body to iterate or recurse over the remainder. You'd also ended up with a nested list using your version but you can use & again to splice in the result, so if you wanted a recursive version of that it would be something like (skipping the base case): fun | flip_all([]): [] | flip_all([Posn(x, y), & rest]): [Posn(y, x), & flip_all(rest)] (not tested, don't have Rhombus available on this system but that should be correct) If you really want flip_first it'd be: fun flip_first([Posn(x, y), & rest]): [Posn(y, x), & rest]
    - Y_Y 2y ago
      In Haskell: flip_one Posn(a,b) = Posn(b,a) flip_first p:ps = flip one : ps flip_all ps = map flip ps To my taste that's a lot nicer
  - soegaard 2y ago
    fun flip_first([Posn(x, y), more, ...]): [Posn(y, x), more, ...]

That syntax suggests the first pair will be flipped, and the rest will just be as they were, i.e. more like flip_first

by arunix 2y ago

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.

Y_Y 2y ago
Typical pattern matching like in Haskell or Prolog wouldn't do this.
- shawn_w 2y ago
  It makes perfect sense if you're used to the pattern matching of Scheme and Racket syntax macros.
  - Y_Y 2y ago
    I guess so, though that might be counterproductive to the goals of Rhombus.
laszlokorte 2y ago
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] If I am correct then the only difference between flipping all and flipping just the first is `...` vs `rest`
- Jtsummers 2y ago
  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]): You'd need to amend the logic of the function body to iterate or recurse over the remainder. You'd also ended up with a nested list using your version but you can use & again to splice in the result, so if you wanted a recursive version of that it would be something like (skipping the base case): fun | flip_all([]): [] | flip_all([Posn(x, y), & rest]): [Posn(y, x), & flip_all(rest)] (not tested, don't have Rhombus available on this system but that should be correct) If you really want flip_first it'd be: fun flip_first([Posn(x, y), & rest]): [Posn(y, x), & rest]
  - Y_Y 2y ago
    In Haskell: flip_one Posn(a,b) = Posn(b,a) flip_first p:ps = flip one : ps flip_all ps = map flip ps To my taste that's a lot nicer
- soegaard 2y ago
  fun flip_first([Posn(x, y), more, ...]): [Posn(y, x), more, ...]