[et] tags/separate

2019-07-03 17:10:54 +02:00
parent 6861215065
commit 77e5f927e7
2 changed files with 278 additions and 0 deletions
--- a/examples/et/4_separate.cpp
+++ b/examples/et/4_separate.cpp
@@ -0,0 +1,150 @@
+#include <cstdio>
+#include <tuple>
+
+/* **** */
+/* tags */
+
+namespace tag {
+
+struct Add;
+struct Mul;
+struct Minus;
+
+}
+
+/* ********** */
+/* expression */
+
+template<typename Op, typename... Operands>
+class Expr {
+	std::tuple<Operands...> _operands;
+
+public:
+	Expr(Operands... operands): _operands{operands...} {}
+
+	template<template<typename> class Evaluator>
+	auto eval() const {
+		return eval<Evaluator>(std::make_index_sequence<sizeof...(Operands)>{});
+	}
+
+private:
+	template<template<typename> class Evaluator, std::size_t... Is>
+	auto eval(std::index_sequence<Is...>) const {
+		return Evaluator<Op>::eval(std::get<Is>(_operands).template eval<Evaluator>()...);
+	}
+};
+
+template<typename T>
+class Value {
+	T _value;
+
+public:
+	Value(T value): _value(value) {}
+
+	template<template<typename> class>
+	auto eval() const { return _value; }
+};
+
+/* *********** */
+/* type traits */
+
+namespace impl {
+template<typename T> struct IsExpr: std::false_type {};
+
+template<typename Op, typename... Operands>
+struct IsExpr<Expr<Op, Operands...>>: std::true_type {};
+
+template<typename T>
+struct IsExpr<Value<T>>: std::true_type {};
+}
+
+template<typename T>
+constexpr bool IsExpr = impl::IsExpr<T>::value;
+
+template<
+	typename LHS, typename RHS,
+	std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
+>
+auto operator+(LHS lhs, RHS rhs) {
+	return Expr<tag::Add, LHS, RHS>{lhs, rhs};
+}
+
+template<
+	typename LHS, typename RHS,
+	std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
+>
+auto operator*(LHS lhs, RHS rhs) {
+	return Expr<tag::Mul, LHS, RHS>{lhs, rhs};
+}
+
+template<
+	typename RHS,
+	std::enable_if_t<IsExpr<RHS>>* = nullptr
+>
+auto operator-(RHS rhs) {
+	return Expr<tag::Minus, RHS>{rhs};
+}
+
+/* ********** */
+/* evaluators */
+
+template<typename> struct EvaluatorElem;
+
+template<>
+struct EvaluatorElem<tag::Add> {
+	template<typename T>
+	static auto eval(T lhs, T rhs) { return lhs + rhs; }
+};
+
+template<>
+struct EvaluatorElem<tag::Mul> {
+	template<typename T>
+	static auto eval(T lhs, T rhs) { return lhs * rhs; }
+};
+
+template<>
+struct EvaluatorElem<tag::Minus> {
+	template<typename T>
+	static auto eval(T rhs) { return -rhs; }
+};
+
+/* *** */
+
+template<typename> struct EvaluatorBool;
+
+template<>
+struct EvaluatorBool<tag::Add> {
+	static auto eval(bool lhs, bool rhs) { return lhs or rhs; }
+};
+
+template<>
+struct EvaluatorBool<tag::Mul> {
+	static auto eval(bool lhs, bool rhs) { return lhs and rhs; }
+};
+
+template<>
+struct EvaluatorBool<tag::Minus> {
+	static auto eval(bool rhs) { return not rhs; }
+};
+
+/* *** */
+
+template<template<typename> class Evaluator, typename Expr>
+auto eval(Expr expr) {
+	return expr.template eval<Evaluator>();
+}
+
+int main() {
+	int volatile v[]{1, 1, 1};
+	int result;
+
+	Value<int> v0{v[0]}, v1{v[1]}, v2{v[2]};
+
+	auto expr = v0 * -(v1 + v2);
+
+	result = eval<EvaluatorElem>(expr);
+	std::printf("evaluator elem: %d\n", result);
+
+	result = eval<EvaluatorBool>(expr);
+	std::printf("evaluator bool: %d\n", result);
+}
--- a/examples/et/4_tags.cpp
+++ b/examples/et/4_tags.cpp
@@ -0,0 +1,128 @@
+#include <cstdio>
+#include <tuple>
+
+/* **** */
+/* tags */
+
+namespace tag {
+
+struct Add {};
+struct Mul {};
+struct Minus {};
+
+}
+
+/* ********** */
+/* expression */
+
+template<typename Op, typename... Operands>
+class Expr {
+	std::tuple<Operands...> _operands;
+
+public:
+	Expr(Operands... operands): _operands{operands...} {}
+
+	template<typename Evaluator>
+	auto eval() const {
+		return eval<Evaluator>(std::make_index_sequence<sizeof...(Operands)>{});
+	}
+
+private:
+	template<typename Evaluator, std::size_t... Is>
+	auto eval(std::index_sequence<Is...>) const {
+		return Evaluator::eval(Op{}, std::get<Is>(_operands).template eval<Evaluator>()...);
+	}
+};
+
+template<typename T>
+class Value {
+	T _value;
+
+public:
+	Value(T value): _value(value) {}
+
+	template<typename>
+	auto eval() const { return _value; }
+};
+
+/* *********** */
+/* type traits */
+
+namespace impl {
+template<typename T> struct IsExpr: std::false_type {};
+
+template<typename Op, typename... Operands>
+struct IsExpr<Expr<Op, Operands...>>: std::true_type {};
+
+template<typename T>
+struct IsExpr<Value<T>>: std::true_type {};
+}
+
+template<typename T>
+constexpr bool IsExpr = impl::IsExpr<T>::value;
+
+template<
+	typename LHS, typename RHS,
+	std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
+>
+auto operator+(LHS lhs, RHS rhs) {
+	return Expr<tag::Add, LHS, RHS>{lhs, rhs};
+}
+
+template<
+	typename LHS, typename RHS,
+	std::enable_if_t<IsExpr<LHS> && IsExpr<RHS>>* = nullptr
+>
+auto operator*(LHS lhs, RHS rhs) {
+	return Expr<tag::Mul, LHS, RHS>{lhs, rhs};
+}
+
+template<
+	typename RHS,
+	std::enable_if_t<IsExpr<RHS>>* = nullptr
+>
+auto operator-(RHS rhs) {
+	return Expr<tag::Minus, RHS>{rhs};
+}
+
+/* ********** */
+/* evaluators */
+
+struct EvaluatorElem {
+	template<typename T>
+	static auto eval(tag::Add, T lhs, T rhs) { return lhs + rhs; }
+
+	template<typename T>
+	static auto eval(tag::Mul, T lhs, T rhs) { return lhs * rhs; }
+
+	template<typename T>
+	static auto eval(tag::Minus, T rhs) { return -rhs; }
+};
+
+struct EvaluatorBool {
+	static auto eval(tag::Add, bool lhs, bool rhs) { return lhs or rhs; }
+	static auto eval(tag::Mul, bool lhs, bool rhs) { return lhs and rhs; }
+	static auto eval(tag::Minus, bool rhs) { return not rhs; }
+};
+
+/* *** */
+
+template<typename Evaluator, typename Expr>
+auto eval(Expr expr) {
+	return expr.template eval<Evaluator>();
+}
+
+int main() {
+	int volatile v[]{1, 1, 1};
+	int result;
+
+	Value<int> v0{v[0]}, v1{v[1]}, v2{v[2]};
+
+	auto expr = v0 * -(v1 + v2);
+
+	result = eval<EvaluatorElem>(expr);
+	std::printf("evaluator elem: %d\n", result);
+
+	result = eval<EvaluatorBool>(expr);
+	std::printf("evaluator bool: %d\n", result);
+}