Re: [Haskell-cafe] Implementing PacMan

Ryan Ingram wrote:

Oops, misread a bit. I thought this was your series of posts, Andrew! But other than that, my points stand :)

Don't you just *hate* it when you reply, and then later realise you missed some small but important detail? ;-) As for your actual content... I will have to meditate deeply on this to comprehend if/why it's helpful here. (As with all good ideas!)

On Wed, Dec 17, 2008 at 12:13 AM, Ryan Ingram wrote:

...

In the last "episode" you talk about an entity's update being a function like:

...

input_state -> (output_state, [event])

for some suitably defined types of input state, output state, and event.

Connecting together functions with types like this is exactly what Reactive does well. You have an event stream representing the behavior of the user during the course of the game, and you use that to construct other values representing the *behavior* of the game. The key difference is that instead of the game's behavior being a set of functions from input to output, it is functions from one behavior to another, eventually culminating in something like

...

-- "user input", "clock tick"; output a new display list at each clock tick game :: Event UserInput -> Event () -> Reactive [RenderCommand]

In fact, I think your analysis in the first message is somewhat right on; this exercise is somewhat like "writing a novel without using the letter 'e'". The benefits you get from a pure language are not necessarily "lack of effects", but rather, "explicitly mentioning where effects happen".

That said, I'm curious where you are going with it. I'd love to see the game running & take a look at your code!

-- ryan