wtfunctional/Notes.md

Title: WTFunctional: Modifying yout WTF-Count using functional programming
Author: Oliver Rümpelein html header:

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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
  • currying => just convenience
  • code example: Pythagoraian triangles, bubble sort
• Phuncy: The pythonic way is functional!
  • Not strictly functional
  • recursion
  • fafco
  • map, fold => example (sum of squares?)

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

    • don't return lists, but iterators!

    • fold with reduce

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

    • The python2 to 3 page states: “Removed reduce(). Use functools.reduce() if you really need it; however, 99 percent of the time an explicit for loop is more readable.”

    • Why use it? => Multi-processing, WTF Count.

      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)
• FunC++tional: 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>