Qing qingwei91

Motivation

Informally, kalman filter helps us to improve estimation of data when measurement is subject to noise. 3 basic concepts to understand

Data collected, it is inaccurate due to noise and also lack of accuracy due to collection mechanism, ie. inaccurate sensor

typically denoted as Z

	sealed trait QueryF[+F[_], A]
	case object QueryStringF extends QueryF[Nothing, String]
	case object QueryBoolF extends QueryF[Nothing, Boolean]
	case class QueryPathF[F[_], A](path: String, next: F[A]) extends QueryF[F, A]

	def typeMatch[A, B](a: A, b: B)(implicit eq: A=:=B) = ()
	val queryString = QueryPath("my", QueryString)
	val queryNestedString = QueryPath("my", QueryPath("oh", QueryString))
	typeMatch(queryString, queryNestedString) // compiles

	// simplified
	sealed trait Query[A]
	case object QueryString extends Query[String]
	case object QueryBool extends Query[Boolean]
	case class QueryPath[A](path: String, next: Query[A]) extends Query[A]
	// sample data
	// {
	// "oh": {
	// "my": "zsh"
	// }

	// Recursive GADT

	sealed trait Query[A]
	case object QueryString extends Query[String]
	case object QueryBool extends Query[Boolean]
	case class QueryPath[A](path: String, next: Query[A]) extends Query[A]

	// sample data

	// {

	object CacheMacroImpl {

	/**
	*
	* @param fnTypeParams - Type params of annotation instance, remember our cache macro is generic `class cache[K, V]`,
	this will capture Seq(K, V)
	* @param cacheExpr - Argument pass to `cache` macro, should be type of `CacheBackEnd[K, V]`
	* @param annotatedDef - Methods that is annotated
	*/
	def expand(fnTypeParams: Seq[Type], cacheExpr: Term.Arg, annotatedDef: Defn.Def): Term = {

	// compiles with `-Ypartial-unification` compiler flag
	val expression = QueryPathF("oh", QueryPathF("my", QueryStringF))

	// does not compile
	Fix(QueryPathF("key", Fix(QueryStringF))