(list)+constructor for List, ~cleaned up some code

Same argument as btree

list.cpp

@@ -11,7 +11,13 @@ template <typename T>
 struct List
 {
   T value;
-  struct List<T> *next;
+  List<T> *next;
+
+  List(T val, List<T> *n)
+  {
+    value = val;
+    next  = n;
+  }
 
   ~List()
   {
@@ -26,19 +32,12 @@ List<T> *append(List<T> *lst, T value)
 {
   List<T> *node;
   if (lst == nullptr)
-  {
-    node        = new List<T>;
-    node->value = value;
-    node->next  = nullptr;
-    return node;
-  }
+    return new List<T>(value, nullptr);
 
   for (node = lst; node->next != nullptr; node = node->next)
     continue;
 
-  node->next        = new List<T>;
-  node->next->value = value;
-  node->next->next  = nullptr;
+  node->next = new List<T>(value, nullptr);
   return lst;
 }
 
@@ -55,12 +54,11 @@ List<T> *reverse(List<T> *lst, List<T> *prev = nullptr)
 }
 
 template <typename T, typename U>
-void map(List<T> *lst, U (*f)(T))
+List<U> *map(List<T> *lst, U (*f)(T))
 {
   if (!lst)
-    return;
-  lst->value = f(lst->value);
-  map(lst->next, f);
+    return nullptr;
+  return new List<U>(f(lst->value), map(lst->next, f));
 }
 
 template <typename T>
@@ -68,7 +66,7 @@ T reduce(List<T> *lst, T (*reducer)(T, T), T init = 0)
 {
   if (!lst)
     return init;
-  if (!init)
+  else if (!init)
     init = lst->value;
   else
     init = reducer(init, lst->value);
@@ -107,25 +105,20 @@ int main(void)
   std::cout << lst << std::endl;
   puts("Reverse list again...");
   printf("Map list with f(x) = 2x: ");
-  map<int, int>(lst = reverse(lst),
-                [](int x)
-                {
-                  return x * 2;
-                });
-  std::cout << lst << std::endl;
-  puts("Reverse map...");
-  map<int, int>(lst,
-                [](int x)
-                {
-                  return x / 2;
-                });
+  auto mapped = map<int, int>(lst = reverse(lst),
+                              [](int x)
+                              {
+                                return x * 2;
+                              });
+  std::cout << mapped << std::endl;
+  delete mapped;
   printf("Sum all numbers in list: ");
   std::cout << reduce<int>(
-                   lst,
-                   [](int a, int b)
-                   {
-                     return a + b;
-                   },
+    lst,
+    [](int a, int b)
+    {
+      return a + b;
+    },
                    0)
             << std::endl;
   printf("Print all even numbers 1..10: ");