Similar to this effort, Eric Niebler's range library [1,2] aims at improving algorithm composability. The range library offers both an eager and lazy API. This is the lazy version (views):

  int sum = accumulate(view::ints(1)
                   | view::transform([](int i) {return i * i;})
                   | view::take(10), 0);

And this the eager (via actions):

   extern std::vector<int> read_data();
   std::vector<int> vi = read_data(); action::unique;
   vi = std::move(vi) | action::sort | action::unique;

Eric puts in a lot of effort to make this library part of the C++ standard (see proposal N4128 [3]).

[1] https://github.com/ericniebler/range-v3

[2] User Manual with code examples: https://ericniebler.github.io/range-v3/index.html

[3] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n412...