Behavior lens for shared refs from local state

1 files changed, 27 insertions, 1 deletions

diff --git a/include/erebos/frp.h b/include/erebos/frp.h
index 587d2b6..b60b29f 100644
--- a/include/erebos/frp.h
+++ b/include/erebos/frp.h
@@ -4,7 +4,6 @@
 #include <memory>
 #include <optional>
 #include <functional>
-#include <type_traits>
 #include <tuple>
 #include <variant>
 
@@ -115,6 +114,8 @@ public:
 		return impl->get(ctime, x);
 	}
 
+	template<typename C> BhvFun<A, C> lens() const;
+
 	const shared_ptr<BhvImpl<A, B>> impl;
 };
 
@@ -135,6 +136,8 @@ public:
 	}
 	Watched<A> watch(function<void(const A &)>);
 
+	template<typename C> BhvFun<monostate, C> lens() const;
+
 	const shared_ptr<BhvSource<A>> impl;
 };
 
@@ -227,4 +230,27 @@ BhvFun<A, C> operator>>(const BhvFun<A, B> & f, const BhvFun<B, C> & g)
 	return impl;
 }
 
+
+template<typename A, typename B>
+class BhvLens : public BhvImpl<A, B>
+{
+public:
+	B get(const BhvCurTime &, const A & x) const override
+	{ return A::template lens<B>(x); }
+};
+
+template<typename A, typename B>
+template<typename C>
+BhvFun<A, C> BhvFun<A, B>::lens() const
+{
+	return *this >> BhvFun<B, C>(make_shared<BhvLens<B, C>>());
+}
+
+template<typename A>
+template<typename C>
+BhvFun<monostate, C> BhvFun<monostate, A>::lens() const
+{
+	return *this >> BhvFun<A, C>(make_shared<BhvLens<A, C>>());
+}
+
 }