Functional curry

libraries/core/src/morpheus/core/functional/CMakeLists.txt

@@ -4,6 +4,7 @@ target_sources(MorpheusCore
     PUBLIC
         FILE_SET HEADERS
         FILES
+            curry.hpp
             function_ref.hpp
             overload.hpp
 )

libraries/core/src/morpheus/core/functional/curry.hpp

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <concepts>
+#include <functional>
+#include <utility>
+
+namespace morpheus::functional
+{
+
+#if (__cpp_explicit_this_parameter >= 202110L)
+
+/// \fn curry
+///     Currying is a technique in which we consider a function takign multuiple arguments and turn it into a function which takes a single argument and
+///     returns a funtion to handle the remaining arguments.
+/// \note
+///     [Applicative: The Forgotten Functional Pattern in C++ - Ben Deane - CppNow 2023](https://youtu.be/At-b4PHNxMg?si=hDI3zgmfPwrrIxoe&t=1313)
+template <typename F, typename... Args>
+constexpr auto curry(F&& f, Args&&... args) -> decltype(auto)
+{
+    if constexpr (std::invocable<F, Args...>)
+        return std::invoke(std::forward<F>(f), std::forward<Args>(args)...);
+    else
+    {
+        return [f = std::forward<F>(f), ...args = std::forward<Args>(args)]<typename Self, typename... As>(this Self&& self, As&&... as) -> decltype(auto)
+        {
+            return curry(std::forward_like<Self>(f), std::forward_like<Self>(args)..., std::forward<As>(as)...);
+        };
+    }
+}
+
+#endif // (__cpp_explicit_this_parameter >= 202110L)
+
+} // namespace morpheus::functional

libraries/core/tests/functional/CMakeLists.txt

@@ -1,4 +1,5 @@
 target_sources(MorpheusCoreTests
     PRIVATE
+        curry.tests.cpp
         function_ref.tests.cpp
 )

libraries/core/tests/functional/curry.tests.cpp

@@ -0,0 +1,59 @@
+#include "morpheus/core/functional/curry.hpp"
+
+#include <catch2/catch_all.hpp>
+
+namespace morpheus::functional
+{
+
+#if (__cpp_explicit_this_parameter >= 202110L)
+
+TEST_CASE("Verify partial application via currying", "[morpheus.functional.curry]")
+{
+    SECTION("Zero parameters")
+    {
+        auto constexpr shouldCall = []()
+        {
+            SUCCEED();
+        };
+        curry(shouldCall);
+    }
+    SECTION("One parameters")
+    {
+        auto constexpr expectedParam1 = 1;
+        auto constexpr identity = [](auto a) { return a; };
+        curry(identity, expectedParam1);
+        REQUIRE(expectedParam1 == identity(expectedParam1));
+    }
+    SECTION("Two parameters")
+    {
+        auto constexpr expectedParam1 = 1;
+        auto constexpr expectedParam2 = 2;
+        auto constexpr add = [](auto a, auto b)
+        {
+            REQUIRE(a == expectedParam1);
+            REQUIRE(b == expectedParam2);
+            return a + b;
+        };
+        auto constexpr add1 = curry(add, expectedParam1);
+        REQUIRE(add1(expectedParam2) == (expectedParam1 + expectedParam2));
+    }
+    SECTION("Three parameters")
+    {
+        auto constexpr expectedParam1 = 1;
+        auto constexpr expectedParam2 = 2;
+        auto constexpr expectedParam3 = 3;
+        auto constexpr add = [](auto a, auto b, auto c)
+        {
+            REQUIRE(a == expectedParam1);
+            REQUIRE(b == expectedParam2);
+            REQUIRE(c == expectedParam3);
+            return a + b + c;
+        };
+        auto constexpr add1 = curry(add, expectedParam1);
+        REQUIRE(add1(expectedParam2, expectedParam3) == (expectedParam1 + expectedParam2 + expectedParam3));
+    }
+}
+
+#endif // (__cpp_explicit_this_parameter >= 202110L)
+
+} // namespace morpheus::functional