Re: [Haskell-cafe] Implementing PacMan

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

On Tue, Dec 16, 2008 at 12:43 PM, Andrew Coppin wrote:

...

What do we think of this, folks?

http://prog21.dadgum.com/23.html

(And the rest in the series, obviously.)

To me, it seems that this plan would *work*... but it wouldn't be very eligant. You'd have the code to respond to user input and move PacMan in one place, the code for collision detection in other place, the code that decides what to *do* about a collision somewhere else, the code for drawing the animations in yet another place... If you wanted to change one game element, you'd have to make changes scattered all over the place. The whole thing seems messy, non-modular and non-composible to my ears.

Thoughts, people?

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