From f3613f96a82c33eb970eda98b457c8a29577e19b Mon Sep 17 00:00:00 2001
From: Paul <pfultz2@yahoo.com>
Date: Fri, 19 Jun 2015 23:43:42 -0400
Subject: [PATCH 1/3] Add if function

---
 CMakeLists.txt |   1 +
 fit/if.h       | 105 +++++++++++++++++++++++++++++++++++++++++++++++++
 test/if.cpp    |  59 +++++++++++++++++++++++++++
 3 files changed, 165 insertions(+)
 create mode 100644 fit/if.h
 create mode 100644 test/if.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4402651..8dbffc9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -74,6 +74,7 @@ add_test_executable(flip)
 add_test_executable(flow)
 add_test_executable(function)
 add_test_executable(identity)
+add_test_executable(if)
 add_test_executable(implicit)
 add_test_executable(indirect)
 add_test_executable(infix)
diff --git a/fit/if.h b/fit/if.h
new file mode 100644
index 0000000..c8700b6
--- /dev/null
+++ b/fit/if.h
@@ -0,0 +1,105 @@
+/*=============================================================================
+    Copyright (c) 2015 Paul Fultz II
+    if_.h
+    Distributed under the Boost Software License, Version 1.0. (See accompanying
+    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+==============================================================================*/
+
+#ifndef FIT_GUARD_IF_H
+#define FIT_GUARD_IF_H
+
+/// if
+/// ==
+/// 
+/// Description
+/// -----------
+/// 
+/// The `if_` function applies a boolen condition to the function.
+/// 
+/// Synopsis
+/// --------
+/// 
+///     template<class IntegralConstant>
+///     constexpr auto if_(IntegralConstant);
+/// 
+/// Requirements
+/// ------------
+/// 
+/// IntegralConstant must be:
+/// 
+///     IntegralConstant
+/// 
+/// Example
+/// -------
+/// 
+///     struct sum_f
+///     {
+///         template<class T, class U>
+///         T operator()(T x, U y) const
+///         {
+///             return x+y;
+///         }
+///     };
+///     assert(fit::if_(sum_f(), 1, 2) == 3);
+/// 
+
+#include <fit/always.h>
+#include <fit/detail/result_of.h>
+#include <fit/detail/forward.h>
+#include <fit/detail/delegate.h>
+#include <fit/detail/move.h>
+#include <fit/detail/static_const_var.h>
+
+namespace fit {
+
+namespace detail {
+
+template<class C, class...>
+struct if_depend
+: C
+{};
+
+template<bool Cond, class F>
+struct if_adaptor : F
+{
+    FIT_INHERIT_CONSTRUCTOR(if_adaptor, F)
+};
+
+template<class F>
+struct if_adaptor<false, F>
+{
+    template<class... Ts>
+    constexpr if_adaptor(Ts&&...)
+    {}
+};
+
+template<bool Cond>
+struct make_if_f
+{
+    constexpr make_if_f()
+    {}
+    template<class F>
+    constexpr if_adaptor<Cond, F> operator()(F f) const
+    {
+        return if_adaptor<Cond, F>(fit::move(f));
+    }
+};
+
+struct if_f
+{
+    constexpr if_f()
+    {}
+    template<class Cond, bool B=Cond::type::value>
+    constexpr make_if_f<B> operator()(Cond) const
+    {
+        return {};
+    }
+};
+
+}
+
+FIT_DECLARE_STATIC_VAR(if_, detail::if_f);
+
+}
+
+#endif
diff --git a/test/if.cpp b/test/if.cpp
new file mode 100644
index 0000000..3fa4db9
--- /dev/null
+++ b/test/if.cpp
@@ -0,0 +1,59 @@
+#include <fit/if.h>
+#include "test.h"
+
+#include <fit/conditional.h>
+
+
+struct is_5
+{
+    template<class T>
+    constexpr bool operator()(T i) const
+    {
+        return i == 5;
+    }
+};
+
+struct is_not_5
+{
+    template<class T>
+    constexpr bool operator()(T i) const
+    {
+        return i != 5;
+    }
+};
+
+template<class F>
+struct test_int
+{
+    template<class T>
+    constexpr bool operator()(T x) const
+    {
+        return fit::conditional(
+            fit::if_(std::is_integral<T>())(F()),
+            fit::always(true)
+        )(x);
+    }
+};
+
+FIT_TEST_CASE()
+{
+    FIT_TEST_CHECK(test_int<is_5>()(5));
+    FIT_TEST_CHECK(test_int<is_5>()(5L));
+    FIT_TEST_CHECK(test_int<is_5>()(5.0));
+    FIT_TEST_CHECK(test_int<is_5>()(6.0));
+
+    FIT_TEST_CHECK(test_int<is_not_5>()(6));
+    FIT_TEST_CHECK(test_int<is_not_5>()(6L));
+    FIT_TEST_CHECK(test_int<is_not_5>()(5.0));
+    FIT_TEST_CHECK(test_int<is_not_5>()(6.0));
+
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(5));
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(5L));
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(5.0));
+    FIT_STATIC_TEST_CHECK(test_int<is_5>()(6.0));
+
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(6));
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(6L));
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(5.0));
+    FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(6.0));
+}

From dfa32f86e41d7d515f68b3393cbb1b55938b03cb Mon Sep 17 00:00:00 2001
From: Paul <pfultz2@yahoo.com>
Date: Fri, 19 Jun 2015 23:52:00 -0400
Subject: [PATCH 2/3] Update test and doc

---
 fit/if.h    | 12 ++++++++----
 test/if.cpp | 25 +++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/fit/if.h b/fit/if.h
index c8700b6..4852c75 100644
--- a/fit/if.h
+++ b/fit/if.h
@@ -34,13 +34,17 @@
 /// 
 ///     struct sum_f
 ///     {
-///         template<class T, class U>
-///         T operator()(T x, U y) const
+///         template<class T>
+///         int operator()(T x, T y) const
 ///         {
-///             return x+y;
+///             return fit::conditional(
+///                 fit::if_(std::is_integral<T>())(fit::_ + fit::_),
+///                 fit::always(0)
+///             )(x, y);
 ///         }
 ///     };
-///     assert(fit::if_(sum_f(), 1, 2) == 3);
+///     assert(sum_f()(1, 2) == 3);
+///     assert(sum_f()("", "") == 0);
 /// 
 
 #include <fit/always.h>
diff --git a/test/if.cpp b/test/if.cpp
index 3fa4db9..9788d25 100644
--- a/test/if.cpp
+++ b/test/if.cpp
@@ -2,6 +2,7 @@
 #include "test.h"
 
 #include <fit/conditional.h>
+#include <fit/placeholders.h>
 
 
 struct is_5
@@ -57,3 +58,27 @@ FIT_TEST_CASE()
     FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(5.0));
     FIT_STATIC_TEST_CHECK(test_int<is_not_5>()(6.0));
 }
+
+struct sum_f
+{
+    template<class T>
+    constexpr int operator()(T x, T y) const
+    {
+        return fit::conditional(
+            fit::if_(std::is_integral<T>())(fit::_ + fit::_),
+            fit::always(0)
+        )(x, y);
+    }
+};
+
+FIT_TEST_CASE()
+{
+    FIT_TEST_CHECK(sum_f()(1, 2) == 3);
+    FIT_TEST_CHECK(sum_f()(1.0, 2.0) == 0);
+    FIT_TEST_CHECK(sum_f()("", "") == 0);
+
+    FIT_STATIC_TEST_CHECK(sum_f()(1, 2) == 3);
+    FIT_STATIC_TEST_CHECK(sum_f()("", "") == 0);
+}
+
+

From 3a9b141284e35c0e6f3717770cb6c7a5738385ce Mon Sep 17 00:00:00 2001
From: Paul <pfultz2@yahoo.com>
Date: Fri, 19 Jun 2015 23:57:03 -0400
Subject: [PATCH 3/3] Add if to the main docs

---
 mkdocs.yml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mkdocs.yml b/mkdocs.yml
index 6494359..63b4e94 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -49,6 +49,7 @@ pages:
     - 'eval': 'eval.md'
     - 'FIT_STATIC_FUNCTION': 'function.md'
     - 'FIT_STATIC_LAMBDA': 'lambda.md'
+    - 'if': 'if.md'
     - 'lift': 'lift.md'
     - 'is_callable': 'is_callable.md'
     - 'pack': 'pack.md'