Functional C++14 λ Syntax

test.cc

#include <iostream>
#include <vector>

template <typename T, typename... TArgs, template <typename...>class C, typename F>
auto fn_map(const C<T,TArgs...>& container, const F& f) {
    using resultType = decltype(f(std::declval<T>()));
    C<resultType> result;
    for (const auto& item : container)
        result.push_back(f(item));
    return result;
}

template <typename TResult, typename T, typename... TArgs,
    template <typename...>class C, typename F>
TResult fn_reduce(const C<T,TArgs...>& container, const TResult& startValue, const F& f)
{
    TResult result = startValue;
    for (const auto& item : container)
        result = f(result, item);
    return result;
}

template <typename T, typename... TArgs, template <typename...>class C, typename F>
C<T,TArgs...> fn_filter(const C<T,TArgs...>& container, const F& f)
{
    C<T,TArgs...> result;
    for (const auto& item : container)
        if (f(item))
            result.push_back(item);
    return result;
}

#define λ(x) [](auto _1){ return (x); }
#define λ2(x) [](auto _1, auto _2){ return (x); }

int main()
{
    using namespace std;
    vector<int> x{1, 2, 3, 4, 5};
    auto even = fn_filter(x, λ(_1 % 2 == 0));
    for(auto &&x : even) {
        cout << x << endl;
    }
    cout << fn_reduce(even, 0, λ2(_1 + _2)) << endl;
    return 0;
}