functional_kata.py

from functools import partial
def reduce(reducing_function, fs, initial_value=None):
    fs = iter(fs)
    v = fs.next() if initial_value is None else initial_value
    for f in fs:
        v = reducing_function(v, f)
    return v
    
square = lambda x: x**2

def s(n):
    res = str(n+0)
    print "s"
    return res

def map_f(f):
    res = partial(map, f)
    print "map_f"
    return res

def compose(*fs):
    def comp2(f,g):
        res = lambda x: f(g(x))
        print "comp2"
        return res
    return reduce(comp2, fs)

# int -> int
# by the way of
# int -> [char] -> [int] -> [char] -> int
# int, str, partial(map(lambda x:int(x)**2)), str
squareDigits = compose(int, map_f(str), map_f(square), s)

################ trace:
# > squareDigits(9119)
# map_f
# map_f
# comp2
# comp2
# comp2
# s
# Traceback:
#    in 
#    in 
#    in 
#    in 
# TypeError: unsupported operand type(s) for ** or pow(): 'str' and 'int'