wtfunctional/Notes.md

71 lines
2.6 KiB
Markdown
Raw Permalink Normal View History

Title: WTFunctional: Modifying yout WTF-Count using functional programming
Author: Oliver Rümpelein
html header: <link rel="stylesheet"
href="http://yandex.st/highlightjs/7.3/styles/default.min.css">
<script src="http://yandex.st/highlightjs/7.3/highlight.min.js"></script>
<script>hljs.initHighlightingOnLoad();</script>
# [%title] #
## 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!
2016-04-25 16:20:31 +02:00
+ Not strictly functional
- recursion
+ fafco
- map, fold => example (sum of squares?)
2016-04-25 16:20:31 +02:00
+ 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
2016-04-25 16:20:31 +02:00
+ 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.”
2016-04-25 16:20:31 +02:00
+ Why use it? => Multi-processing, WTF Count.
```python
a = list(range(10))
b = 0
for i in a:
b += i**2
print(b)
```
vs.
```python
from functools import reduce
print(reduce(lambda x,y: x+y,map(lambda x: x**2,range(10))))
```
2016-04-25 16:20:31 +02:00
+ 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>`