Re: [ats-lang-users] Can you pass !(&viewtypevar) as an argument that can be mutated?

[Hans V. <keg...@gm...>]

fun oneLoop (ui : &ui >> _) : void =

solved it. Thank you Hongwei!

On Fri, Dec 3, 2021 at 8:38 PM Hans Vejle <keg...@gm...> wrote:
>
> Hello Dr. Xi & friends,
>
> I am a very stupid man when it comes to types, and I'm working on my
> first ATS project using SDL and Emscripten. It worked right away,
> which felt amazing! However, I'm trying to understand how I can pass
> around a var like I do !type to avoid consuming the linear proof and
> still be able to mutate the argument. (Perhaps assuming this makes
> sense is my mistake.)
>
> I found a few posts on this list about creating "takeout/putback"
> prvals, as well as this excellent post
> https://bluishcoder.co.nz/2011/04/25/sharing-linear-resources-in-ats.html
> which came very close, but unfortunately I was unable to figure out
> how to apply it to my problem of passing around a reference to a var
> of a viewtype whose proofs I want to avoid consuming while still being
> able to mutate the argument.
>
> The below compiles if I don't attempt to set any field of ui, but If I
> uncomment either the ui.dimensions or ui.running :=, I get an error
> that seems to indicate that the l1 proof for ui was consumed.
>
> 10062(line=333, offs=5) -- 10064(line=333, offs=7): error(3): unsolved
> constraint: C3NSTRprop(C3TKmain(); S2Eeqeq(S2Evar(l1$9081(14901));
> S2Evar(l1$9028(14847))))
> src/main.dats: 10062(line=333, offs=5) -- 10064(line=333, offs=7):
> error(3): unsolved constraint for var preservation
> typechecking has failed: there are some unsolved constraints: please
> inspect the above reported error message(s) for information.
>
> This makes sense to me since I'm passing &ui, not !ui. If I change the
> argument of oneLoop to !ui (whether ui is an @ or '), I get this
> error:
>
> 9865(line=324, offs=34): error(3): a non-proof component is replaced
> of the type: [S2Ecst(bool)].
>
> I assume this is because the argument is no longer mutable.
>
> Should I not be trying to use a viewtype var this way?
>
> Thank you in advance,
> Hans
>
> PS: Bonus question: Is there a way in ATS to do the matching of
> SDL_Event below as a switch statement (i.e. pattern-matching on
> $extval constants)?
>
> ---
>
> typedef dimensions =
>  @{ width = int
>   , height = int
>   , refreshRate = int
>   }
>
> viewtypedef ui (l1 : addr, l2 : addr, l3 : addr) =
>  @{ window = SDL_Window l1
>   , renderer = SDL_Renderer l2
>   , font = TTF_Font l3
>   , dimensions = dimensions
>   , running = bool
>   }
>
> viewtypedef ui = [l1, l2, l3 : agz] ui(l1, l2, l3)
>
> // (SDL_Window/Renderer/TTF_Font are addr absviewtypes + agz
> viewtypedef as you'd expect)
>
> typedef callback = (&ui) -<fun1> void
>
> extern fun emscripten_set_main_loop_arg (func : callback, arg : &ui,
> fps : int, simulate_infinite_loop : bool) : void = "mac#"
>
> fun oneLoop (ui : &ui) : void =
>   let
>     var e : SDL_Event
>     val () = e.type := $Unsafe.cast 0
>     var pollRet : int = SDL_PollEvent e
>     val () =
>       while (pollRet = 1) (
>         let
>           val () =
>             if e.type = SDL_MOUSEMOTION
>               then ()
>               else if e.type = SDL_WINDOWEVENT
>                 then () // ui.dimensions := getWindowDimensions ui.window
>                 else if e.type = SDL_QUIT
>                   then () // ui.running := false
>                   else ()
>         in
>           pollRet := SDL_PollEvent e
>         end
>       )
>     // val () = draw ui
>   in
>     ()
>   end
>
> implement main0 () =
>   let
>    ...
>     var ui : ui (null, null, null)
>     val () = ui.running := true
>     val () = ui.dimensions := getDesktopDimensions ()
>     val () = ui.window := SDL_CreateWindow ("risk", 0, 0,
> ui.dimensions.width, ui.dimensions.height,
> SDL_WINDOW_SHOWN_RESIZABLE_OPENGL_HIGHDPI)
>     val () = ui.renderer := SDL_CreateRenderer (ui.window, ~1,
> SDL_RENDERER_ACCELERATED)
>     val () = ui.font := TTF_OpenFont ("fonts/UbuntuMono-R.ttf", 64)
>     val ((* main loop *)) = emscripten_set_main_loop_arg(oneLoop, ui, 0, true)
>     val () = SDL_DestroyRenderer ui.renderer
>     val () = SDL_DestroyWindow ui.window
>     val () = TTF_CloseFont ui.font
>     val () = TTF_Quit ()
>     val () = SDL_FreeCursor cursorArrow
>     val () = SDL_Quit ()
>   in
>     ()
>   end