Add pong example;

pong.lua

@@ -0,0 +1,136 @@
+local Rx = require 'rx'
+require 'rx-love'
+
+-- Map parameters
+local width = 800
+local height = 600
+local border = 10
+
+-- Player parameters
+local paddleWidth = 20
+local paddleHeight = 80
+local paddleSpeed = 500
+
+-- Ball parameters
+local ballSize = 20
+
+-- Maps keys to players and directions
+local keyMap = {
+  w = {'player1', -1},
+  s = {'player1', 1},
+  up = {'player2', -1},
+  down = {'player2', 1}
+}
+
+local state
+
+-- Declare initial state of game
+function love.load()
+  state = {
+    ball = {
+      x = width / 2 - ballSize / 2,
+      y = height / 2 - ballSize / 2,
+      width = ballSize,
+      height = ballSize,
+      direction = 3 * math.pi / 4,
+      speed = 400
+    },
+    player1 = {
+      x = border,
+      y = height / 2 - paddleHeight / 2,
+      width = paddleWidth,
+      height = paddleHeight
+    },
+    player2 = {
+      x = width - (border + paddleWidth / 2),
+      y = height / 2 - paddleHeight / 2,
+      width = paddleWidth,
+      height = paddleHeight
+    }
+  }
+end
+
+-- Helper functions
+local function identity(...) return ... end
+local function const(val) return function() return val end end
+local function dt() return love.update:getValue() end
+local function move(player, direction)
+  state[player].y = state[player].y + direction * paddleSpeed * dt()
+end
+
+-- Respond to key presses to move players
+for _, key in pairs({'up', 'down', 'w', 's'}) do
+  love.update
+    :map(const(key))
+    :filter(love.keyboard.isDown)
+    :map(function(key)
+      return unpack(keyMap[key])
+    end)
+    :subscribe(move)
+end
+
+-- Move ball
+love.update
+  :skip(1)
+  :subscribe(function()
+    state.ball.x = state.ball.x + math.cos(state.ball.direction) * state.ball.speed * dt()
+    state.ball.y = state.ball.y + math.sin(state.ball.direction) * state.ball.speed * dt()
+  end)
+
+-- Collision on top and bottom
+love.update
+  :filter(function()
+    return state.ball.y < 0 or state.ball.y > height - ballSize
+  end)
+  :subscribe(function()
+    state.ball.direction = -state.ball.direction
+    state.ball.y = math.max(state.ball.y, 0)
+    state.ball.y = math.min(state.ball.y, height - ballSize)
+  end)
+
+-- Paddle collision
+love.update
+  :map(function()
+    local left = state.ball.x - ballSize / 2 < state.player1.x + paddleWidth and
+      state.ball.y + ballSize / 2 > state.player1.y and
+      state.ball.y + ballSize / 2 < state.player1.y + paddleHeight
+
+    local right = state.ball.x + ballSize / 2 > state.player2.x and
+      state.ball.y + ballSize / 2 > state.player2.y and
+      state.ball.y + ballSize / 2 < state.player2.y + paddleHeight
+
+    return left and 'left' or (right and 'right' or nil)
+  end)
+  :compact()
+  :subscribe(function(side)
+    local x, y = math.cos(state.ball.direction), math.sin(state.ball.direction)
+    x = -x
+    state.ball.direction = math.atan2(y, x)
+    if side == 'left' then
+      state.ball.x = math.max(state.ball.x, state.player1.x + paddleWidth + ballSize / 2)
+    elseif side == 'right' then state.ball.x = math.max(state.ball.x, state.player1.x + paddleWidth)
+      state.ball.x = math.min(state.ball.x, state.player2.x - ballSize / 2)
+    end
+
+    state.ball.speed = state.ball.speed + 20
+  end)
+
+-- Game over
+love.update
+  :filter(function()
+    return state.ball.x < 0 or state.ball.x + ballSize > width
+  end)
+  :subscribe(love.load)
+
+-- Draw state
+love.draw:subscribe(function()
+  local g = love.graphics
+
+  g.setColor(0, 0, 0)
+  g.rectangle('fill', 0, 0, width, height)
+
+  g.setColor(255, 255, 255)
+  g.rectangle('fill', state.player1.x, state.player1.y, state.player1.width, state.player1.height)
+  g.rectangle('fill', state.player2.x, state.player2.y, state.player2.width, state.player2.height)
+  g.rectangle('fill', state.ball.x, state.ball.y, state.ball.width, state.ball.height)
+end)