Add queries example

examples/luau/entities/basics.luau

@@ -39,7 +39,7 @@ for entity, p in world:query(Position) do
     print(`{entity}: \{{p.X}, {p.Y}, {p.Z}\}`)
 end
 
--- Output
+-- Output:
 --  {10, 20, 30}
 --  Alice: {10, 20, 30}
 --  Bob: {40, 50, 60}

examples/luau/entities/hierarchy.luau

@@ -111,7 +111,7 @@ do
     iterate(sun, Vector3.zero)
 end
 
--- Output
+-- Output:
 --  Child of Earth? true
 --  Sun
 --  {1, 1, 1}

examples/luau/queries/basics.luau

@@ -0,0 +1,75 @@
+local ecs = require("@jecs")
+local world = ecs.World.new()
+
+local Position = world:component()
+local Velocity = world:component()
+local Name = world:component()
+
+local Vector3
+do
+    Vector3 = {}
+    Vector3.__index = Vector3
+
+    function Vector3.new(x, y, z)
+        x = x or 0
+        y = y or 0
+        z = z or 0
+        return setmetatable({ X = x, Y = y, Z = z }, Vector3)
+    end
+
+    function Vector3.__add(left, right)
+        return Vector3.new(
+            left.X + right.X,
+            left.Y + right.Y,
+            left.Z + right.Z
+        )
+    end
+
+    function Vector3.__mul(left, right)
+        if typeof(right) == "number" then
+            return Vector3.new(
+                left.X * right,
+                left.Y * right,
+                left.Z * right
+            )
+        end
+        return Vector3.new(
+            left.X * right.X,
+            left.Y * right.Y,
+            left.Z * right.Z
+        )
+    end
+
+    Vector3.one = Vector3.new(1, 1, 1)
+    Vector3.zero = Vector3.new()
+end
+
+-- Create a few test entities for a Position, Velocity query
+local e1 = world:entity()
+world:set(e1, Name, "e1")
+world:set(e1, Position, Vector3.new(10, 20, 30))
+world:set(e1, Velocity, Vector3.new(1, 2, 3))
+
+local e2 = world:entity()
+world:set(e2, Name, "e2")
+world:set(e2, Position, Vector3.new(10, 20, 30))
+world:set(e2, Velocity, Vector3.new(4, 5, 6))
+
+-- This entity will not match as it does not have Position, Velocity
+local e3 = world:entity()
+world:set(e3, Name, "e3")
+world:set(e3, Position, Vector3.new(10, 20, 30))
+
+-- Create an uncached query for Position, Velocity.
+for entity, p, v in world:query(Position, Velocity) do
+    -- Iterate entities matching the query
+    p.X += v.X
+    p.Y += v.Y
+    p.Z += v.Z
+
+    print(`{world:get(entity, Name)}: \{{p.X}, {p.Y}, {p.Z}}`)
+end
+
+-- Output:
+--  e2: {14, 25, 36}
+--  e1: {11, 22, 33}