diff --git a/src/ecs.lua b/src/ecs.lua
new file mode 100644
index 0000000..14db8fd
--- /dev/null
+++ b/src/ecs.lua
@@ -0,0 +1,170 @@
+local ENTITY_STORAGE = {}
+local PLACEHOLDER = {}
+
+ecs = { }
+
+function ecs.addEntity(entity)
+	ENTITY_STORAGE[entity] = true
+end
+
+---@return any
+function ecs.field()
+	return PLACEHOLDER
+end
+
+function allKeysIncluded(entity, filter)
+	for k, _ in pairs(filter) do
+		if not entity[k] then
+		    return false
+		end
+	end
+	return true
+end
+
+function allFiltersMatch(entity, filters)
+	for _, filter in pairs(filters) do
+		if not allKeysIncluded(entity, filter) then
+		    return false
+		end
+	end
+	return true
+end
+
+---@generic T
+---@param shape T
+---@return fun(): T[]
+function ecs.buildEntityFilter(shape)
+	local filters = {shape}
+	return function()
+		-- TODO? Cache all this?
+		local ret = {}
+		for entity,_ in pairs(ENTITY_STORAGE) do
+			if allFiltersMatch(entity, filters) then
+				ret[#ret + 1] = entity;
+			end
+		end
+		return ret
+	end
+end
+
+---@generic T
+---@return fun(): T[]
+function ecs.buildRequiredFields(...)
+	local filters = arg
+	return function()
+		-- TODO? Cache all this?
+		local ret = {}
+		for entity,_ in pairs(ENTITY_STORAGE) do
+			if allKeysIncluded(entity, filters) then
+				ret[#ret + 1] = entity;
+			end
+		end
+		return ret
+	end
+end
+-- --@overload fun(tShape: `T`): fun(callback: fun(componentT: `T`))
+
+---@generic T
+---@generic U
+---@generic V
+---@generic W
+---@param tShape T
+---@param uShape U?
+---@param vShape V?
+---@param wShape W?
+---@return fun(callback: fun(componentT: T, componentU: U, componentV: V, componentW: W))
+function ecs.entitiesWithShapes(tShape, uShape, vShape, wShape)
+	return function()
+	end
+end
+
+--- Returns a function that accepts a callback. This callback will receive one argument for each Shape provided.
+---
+---@generic T
+---@generic TKey
+---@generic U
+---@generic UKey
+---@generic V
+---@generic VKey
+---@generic W
+---@generic WKey
+---@param tShape { [TKey]: T }
+---@param uShape { [UKey]: U }?
+---@param vShape { [VKey]: V }?
+---@param wShape { [WKey]: W }?
+---@return fun(callback: fun(componentT: T, componentU: U, componentV: V, componentW: W))
+function ecs.entitiesWithShapes2(tShape, uShape, vShape, wShape)
+	local filters = {tShape, uShape, vShape, wShape}
+	return function(callback)
+		-- TODO? Cache all this?
+		local ret = {}
+		for entity,_ in pairs(ENTITY_STORAGE) do
+			if allFiltersMatch(entity, filters) then
+				callback(entity, entity, entity, entity)
+			end
+		end
+		return ret
+	end
+end
+
+local f = ecs.field()
+
+---@alias XYPair { x:number, y: number }
+
+---@type XYPair
+local XYPair = { x = f, y = f }
+
+local HasPosition = { position = XYPair }
+local HasVelocity = { velocity = XYPair }
+
+local entIt = ecs.entitiesWithShapes(HasPosition, HasVelocity)
+entIt(function(hasPos, hasVel)
+	hasPos.position.x = hasPos.position.x + hasVel.velocity.y
+end)
+
+local entIt2 = ecs.entitiesWithShapes2(HasPosition)
+entIt2(function(position, velocity)
+	---@type number
+	local num = 0
+	num = position.x
+	num = velocity.z
+	print(num)
+end)
+
+---@return fun(callback: fun(T))
+function ecs.entitiesWithFields(...)
+	local filters = {...}
+	return function(callback)
+		-- TODO? Cache all this?
+		for entity,_ in pairs(ENTITY_STORAGE) do
+			if allKeysIncluded(entity, filters) then
+				callback(entity)
+			end
+		end
+	end
+end
+
+---@type unknown
+function ecs.shape(...)
+	local shape = {}
+	for _,incomingShape in ipairs(arg) do
+		for k,v in pairs(incomingShape) do
+			shape[k] = v
+		end
+	end
+	return shape
+end
+
+local exampleEntity = {
+	position = { x = 0, y = 0 },
+	velocity = { x = 1, y = 1 }
+}
+
+ecs.addEntity(exampleEntity)
+
+---@type fun(system: fun(entity: { position: XYPair, velocity: XYPair }))
+local forEachPosVel = ecs.entitiesWithFields('position', 'velocity')
+
+forEachPosVel(function(hasVelPos)
+	print(hasVelPos.velocity.x)
+end)
\ No newline at end of file