Grid Reactors for Purescript
Reactors are values enabling the creation of time-based animations, simulations, and interactive programs, as per Pyret Documentation. This particular library brings the fun of reactors into Purescript, allowing you to create simple grid-based games in 3 steps:
- Tell the reactor the initial state of your game, e.g. the positions of the player and the enemies.
- Explain how a state can be drawn on a grid, using our intuitive DSL.
- Finally, describe how the state changes depending on incoming mouse and keyboard input events, and if there is a background clock, how the state changes on the ticks.
Then you just call runReactor [your reactor] and you're set! The reactor listens for the events, runs the clock, and does the rendering using a Halogen component. Declarative programming at its best.
Example
If you thought we've skipped some details, you're wrong — that really was all there's to it. Let's see a simple example: a 'game' in which the user can move a blue dot using arrow keys.
import Reactor.Action
(executeDefaultBehavior, modify_, preventDefaultBehavior, utilities)
import Reactor.Events (KeypressEvent(..))
import Reactor.Graphics.Colors as Color
import Reactor.Graphics.CoordinateSystem
(CoordinateSystem, grid, moveDown, moveLeft, moveRight, moveUp, wrt)
import Reactor.Graphics.Drawing (fill, cell)
import Reactor.Types (Reactor)
type World =
{ player :: CoordinateSystem { x :: Number, y :: Number }
, paused :: Boolean
}
reactor :: forall m. Reactor m World
reactor =
{ init: { dot: { x: 0, y: 0 } `wrt` grid, paused: true }
, draw: \{ dot } -> fill Color.blue400 $ cell dot
, onTick: \_ -> pure unit
, onKey: \(KeypressEvent key _) -> do
{ bound } <- utilities
case key of
"ArrowLeft" -> do
modify_ \w@{ player } ->
w { player = bound $ moveLeft player }
preventDefaultBehavior
"ArrowRight" -> do
modify_ \w@{ player } ->
w { player = bound $ moveRight player }
preventDefaultBehavior
"ArrowDown" -> do
modify_ \w@{ player } ->
w { player = bound $ moveDown player }
preventDefaultBehavior
"ArrowUp" -> do
modify_ \w@{ player } ->
w { player = bound $ moveUp player }
preventDefaultBehavior
_ -> executeDefaultBehavior
, onMouse: \_ -> executeDefaultBehavior
}We ignore the mouse events, and we pause the clock — the only way the state changes is through the onKey event handler. In the draw function, given a position of a dot, we fill a blue cell on the grid in the same place.
