ECS DSL primer

// container component
// a constructor is automatically generated for a component that has the same order with field declaration
// for example, for position component following ctor is generated: (x, y, z)
component position
	float x
	float y
	float z
	
	
// component with single field
component float health


// tag component
tag component destroyed


// event definition
event damageTaken
	float damage


// entity generation
entity newSpaceship
	postion = (10, 5, 6)
	health = 100
	

// regular system
system positionSystem

	// entity signature filters
	all: position
	any: x, y
	none: z
	
	// read component
	pos = entity.position
	
	// write component
	entity.position = new pos
		x: 5
		y: 4
		z: 3
	
	entity.position = pos + (1, 2, 3)
	
	// this is also possible
	entity.position.x = 10
	
	// this too
	// if entity doesn't have a health, it will be added and then set
	entity.health = 5
	
	// add component
	add destroyed to entity
	
	add foo to entity
		bar: baz
		
	// remove component
	remove position from entity
	
	// raise an event
	raise damageTaken
	
		// sender -> target
		fooEntity -> barEntity
		
		// values
		damage: 5
	

// reactive system
reactive system positionChangeSystem 

	// define which component this system reacts to
	reacts to position

	// entity signature filters
	all: position
	any: foo, bar
	none: baz
	
	oldPos = reaction.old
	newPos = reaction.new
	

// event listener system
listener system damageTakenSystem

	// define which event this system listens for
	listens to damageTaken
	
	// entity signature filters for the sender entity
	sender:
		all: position
	
	// entity signature filters for the target entity
	target:
		all: position
	
	// get the sender entity
	sender = event.sender
	
	// get the target entity
	target = event.target
	
	// read and operate on event values
	origin.health -= event.damage

for your "damageTakenSystem", wouldn't you want to filter by entities that have "health" component. what happens when en entity with position component but no health component receives damage?

Suggestion: you could consider making use of the "!" to allow/disallow component creation by Setters. i.e :

spaceship.health = 5 // should throw error if health component is not part of spaceship.
spaceship.health! = 5 // will create health component if it doesnt exist. no error.

Yes, the gameplay semantics are way off, this is more of a primer for how such a language would look like.