yin wrote:
Hello all!
I'm doing a 3D simulation. Now I need something like variables in imperative languages. My mainLoop check for new events and renders scene. To use input for controling camera position I need variables. An equivalent code in C:
void main_loop() { int loop_num = 0; bool run = 1; SDLEvent e;
while(run) { while(SDL_PollEvent(&e)) { if(e.type == SDL_KeyDown) { if(... == SDLK_Left) camera_pos_x--; } else if ... ... }
drawScene();
loop_num++; } }
How to implement camera_pos_x, y and z as variables, which chage values in run? This is only simplified example, but it's important to implement it in as most imperative form as possible.
Then you want IORef. http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data.IORef.html Consider, however, that this kind of construct can be done without mutable variables. (warning, made-up code ahead) main = loop 0 0 0 -- initial values where loop loop_num xpos ypos = do e <- pollEvent let xpos' = <calculate new xpos> ypos' = <calculate new ypos> someActionInvolvingPosition xpos' ypos' when breakCondition (return ()) loop (loop_num+1) xpos' ypos'