wtfunctional/Notes.md

WTFunctional: Modifying your WTF-Count using functional programming

Content

• Dafunc? Understanding functional programming with Haskell.
  • no side-effects, no mutability => maintainability
  • recursion
  • functions as first class “objects”: i.e. C++, 5; is a valid statement
  • lambdas
  • lists, maps, filters, folds => readability, less code reproduction, threadsafety…
  • currying => just convenience
  • code example: Pythagoraian triangles.
• Phuncy: The pythonic way is functional!
  • Not strictly functional
  • recursion, fafco
  • lambda syntax
  • map, fold => example (sum of squares?)

    • python lambda syntax: lambda a,b: a+b

    • fold with reduce

    • don't return lists, but iterators!

    • Note: 2: map, filter, reduce 3: map, filter, functools.reduce()

         however, 99 percent of the time an explicit for loop is more
         readable.```
      Why use it? => Multi-processing!
      

      a = list(range(10))

      b = 0 for i in a: b += i**2 print(b)

      vs.
      

      from functools import reduce print(reduce(lambda x,y: x+y,map(lambda x: x**2,range(10))))

  • currying: not really, but binding via lambdas or functools.partial() or https://mtomassoli.wordpress.com/2012/03/18/currying-in-python/
  • decorators!
  • still FP, has advantages and is heavily used, i.e. in genomics (works on tons of lengthy lists)
• FunCtional++: On the fast lane
  • "Classical" C++ has some functional stuff, bust i.e. no lambdas (hardly usable)
  • Changed with the new C++11-standard
  • Buzzwords:
    • map defines a Datatype in C++!
    • lambdas in C++ [](int x, int y) { return a<b;} ; [] can be used to capture variables, i.e. by reference or value
    • std::for_each from algorithm: Apply void fun(T &a) to iterator containing T values
    • std::transform from algorithm: same as for_each, but stores return value in another range
    • std::accumulate from numeric: Wants binary operation, i.e. std::minus<int>