Functional programming tools in Python. Declarative programming style elements.

10_list_comprehension_map.py

### List comprehension: map (+filter) part of map-reduce

## map: Mj <- Lj + 10 for all j
M = [x+10 for x in L]

## filter: select lines from file that start with 'p' and strip newlines
lines = [line.rstrip() for line in open('file.txt') if line[0]=='p']

20_fun_state_retention.py

### State retention in functions: FP alternative to class attributes.
###  NOTE: this is the idea of scala actor implementation.
###  NOTE2: functools.partial provides an alternative.

## Closure (factory) function
def maker(N):
  def action(X):
    return X**N
  return action
## N is being retained similarly to a class attribute
f = maker(2)
f(3) # 9
g = maker(3)
g(3) # 27
f(3) # still 9

## with lambda
def func():
  x = 4
  action = (lambda n: x**n) ## x remembered from enclosing scope
  return action
x = func()
x(2) # 4**2