Haskell

The idea is quite simple. The Standard Template (STL) has more than 100 algorithms for searching, counting, and manipulating ranges and their elements. With C++17, 69 are overloaded, and a few new ones are added. The overloaded and new algorithm can be invoked with a so-called execution policy. By using the execution policy, you can specify whether the algorithm should run sequentially, parallel, or parallel and vectorized.

Monads in C++? What a strange name for a post. But it's not so strange. With std::optional, C++17 gets a monad. The ranges library from Eric Niebler and the extended futures are also monads. For both, we can hope for in C++20.

We stay in the year 2020. With high probability, we will get concepts. Of course, waterproof statements about the future are challenging, but the statement is from Bjarne Stroustrup (Meeting C++ 2016 at Berlin).

A small-time jump, and we are in the year 2020. C++ will get - as far as the future is predictable - the new ranges library. Thanks to Eric Nieblers library, working with the Standard Template Library (STL) will become more comfortable and powerful.

With fold expressions, you can implement Haskell functions foldl, foldr, foldl1, and foldr1 directly in C++. These four functions successively reduce a list to a single value.

The remaining three characteristics of functional programming are told quite quickly: Recursion, manipulation of lists, and lazy evaluation.

Pure functions are pretty similar to mathematical functions. They are the reason that Haskell is called a pure functional programming language.

A key to purely functional languages is that their data are immutable. Therefore, assignments such as x= x+1 or ++x are not possible in the purely functional language Haskell. The consequence is that Haskell supports no loops like for, while, or until. They are based on the modification of a loop variable. Haskell does not modify existing data; Haskell creates new data when needed and reuses the old ones.

Which functional feature can we expect with C++17, and for which functional feature can we hope with C++20? This is precisely the question I will concisely answer in this post.