Add tasks for all the new languages

Task/Flatten-a-list/Nim/flatten-a-list.nim

@@ -0,0 +1,34 @@
+type
+  TreeList[T] = ref TTreeList[T]
+  TTreeList[T] = object
+    case isLeaf: bool
+    of true:  data: T
+    of false: list: seq[TreeList[T]]
+
+proc L[T](list: varargs[TreeList[T]]): TreeList[T] =
+  var s: seq[TreeList[T]] = @[]
+  for x in list: s.add x
+  TreeList[T](isLeaf: false, list: s)
+
+proc N[T](data: T): TreeList[T] =
+  TreeList[T](isLeaf: true, data: data)
+
+proc `$`[T](n: TreeList[T]): string =
+  if n.isLeaf: result = $n.data
+  else:
+    result = "["
+    for i, x in n.list:
+      if i > 0: result.add ", "
+      result.add($x)
+    result.add "]"
+
+proc flatten[T](n: TreeList[T]): seq[T] =
+  if n.isLeaf: result = @[n.data]
+  else:
+    result = @[]
+    for x in n.list:
+      result.add flatten x
+
+var x = L(L(N 1), N 2, L(L(N 3, N 4), N 5), L(L(L[int]())), L(L(L(N 6))), N 7, N 8, L[int]())
+echo x
+echo flatten(x)