71 lines
2.6 KiB
Markdown
71 lines
2.6 KiB
Markdown
Title: WTFunctional: Modifying yout WTF-Count using functional programming
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Author: Oliver Rümpelein
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# [%title] #
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## Content ##
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* Dafunc? Understanding functional programming with Haskell.
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+ no side-effects, no mutability => maintainability
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+ recursion
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+ functions as first class “objects”: i.e. C++, 5; is a valid statement
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+ lambdas
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+ lists, maps, filters, folds
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+ currying => just convenience
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+ code example: Pythagoraian triangles, bubble sort
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* Phuncy: The pythonic way is functional!
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+ Not strictly functional
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- recursion
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+ fafco
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- map, fold => example (sum of squares?)
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+ python lambda syntax: lambda a,b: a+b
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+ don't return lists, but iterators!
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+ fold with reduce
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+ Note: 2: map, filter, reduce, list comprehension
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3: map, filter, functools.reduce(), list comprehension
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+ The python2 to 3 page states:
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“Removed `reduce()`. Use `functools.reduce()` if you really need it;
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however, 99 percent of the time an explicit `for` loop is more
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readable.”
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+ Why use it? => Multi-processing, WTF Count.
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```python
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a = list(range(10))
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b = 0
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for i in a:
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b += i**2
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print(b)
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```
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vs.
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```python
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from functools import reduce
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print(reduce(lambda x,y: x+y,map(lambda x: x**2,range(10))))
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```
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+ currying: not really, but binding via lambdas or functools.partial() or
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https://mtomassoli.wordpress.com/2012/03/18/currying-in-python/
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+ decorators!
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+ still FP has advantages and is heavily used, i.e. in genomics (works on
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tons of lengthy lists)
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* FunC++tional: On the fast lane
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+ "Classical" C++ has some functional stuff, bust i.e. no lambdas (hardly usable)
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+ Changed with the new C++11-standard
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+ Buzzwords:
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+ `map` defines a Datatype in C++!
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+ lambdas in C++
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```[](int x, int y) { return a<b;} ;```
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[] can be used to capture variables, i.e. by reference or value
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+ `std::for_each` from `algorithm`: Apply `void fun(T &a)` to iterator
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containing `T` values
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+ `std::transform` from `algorithm`: same as for_each, but stores return
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value in another range
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+ `std::accumulate` from `numeric`: Wants binary operation, i.e. `std::minus<int>`
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