#!/usr/bin/env python

# import required modules:
#  note that the path to the module htkmfc must be included in the
#  PYTHONPATH environment variable.
#
import os
import sys
from functools import reduce

# function: square
#
# compute the square of a number
#
def square(x):
    return(x ** 2)

# function: cube
#
# compute the cube of a number
#
def cube(x):
    return(x ** 3)

# function: mymap
#
# a general mapping function
#
def mymap(aFunc, aSeq):
    result = []
    for x in aSeq: result.append(aFunc(x))
    return result

# main program
#
def main(argv):

    # imperative: compute the sum of squares
    #
    items = [1, 2, 3, 4, 5]
    squared = []
    for x in items:
        squared.append(x ** 2)
    print("imperative:")
    print(squared)
    print("")

    # functional: use map
    #
    print("functional (map):")    
    print(list(map(square, items)))
    print("")

    # functional: use lambda
    #
    print("functional (lambda):")    
    print(list(map((lambda x: x ** 2), items)))
    print("")

    # functional: list of functions
    #
    print("functional (lambda with function lists):")    
    funcs = [square, cube]
    for r in range(5):
        value = map(lambda x: x(r), funcs)
        print(list(value))
    print("")
    print("")

    # functional: mymap
    #
    print("functional (mymap):")    
    print(list(map(square, [1, 2, 3])))
    print(mymap(square, [1, 2, 3]))
    print("")

    # functional: multiple lists
    #
    x = [1, 2, 3]
    y = [4, 5, 6]
    from operator import add
    print("functional (multiple lists):")    
    print(x, "+", y, '=', list(map(add, x, y)))
    print("")

    # filter: numbers less than zero
    #
    print("list (numbers less than zero):")    
    print(list(range(-5,5)))
    print(list(filter((lambda x: x < 0), range(-5,5))))
    print("")

    # lists: intersecting two lists
    #
    a = [1, 2, 3, 5, 7, 9]
    b = [2, 3, 5, 6, 7, 8]
    print("list (intersecting two lists using filter):")    
    print(a)
    print(b)
    print(list(filter(lambda x: x in a, b)))
    print("")

    # lists: list comprehension
    #
    print("list (intersecting two lists using list comprehension):")    
    print(a)
    print(b)
    print([x for x in a if x in b])
    print("")

    # reduce: compute the sum
    #
    print("reduce (compute the sum):")    
    print([1, 2, 3, 4])
    print("sum product = ", reduce((lambda x, y: x * y), [1, 2, 3, 4]))
    print("sum ratio = ", reduce((lambda x, y: x / y), [1, 2, 3, 4]))
    print("sum new ratio = ", reduce((lambda x, y: y / x), [1, 2, 3, 4]))
    print("")

# begin gracefully
#
if __name__ == "__main__":
    main(sys.argv[0:])

#
# end of file