Implement mapping data structure and "classes" using functions and lists

fp.py

## Author: Alexey Kachayev
## Email: [email protected]
## Talk: "Functional programming with Python", UA PyCon 2012
## URL: http://ua.pycon.org/static/talks/kachayev/index.html#/

###############################################
## Imitate dictionary functionality
###############################################

def dict_pair((key, value)):
    return lambda k: value if k == key else None

def dict_new(*items):
    return dict_update(dict_pair((None, None)), *items)

def dict_update(base, *updates):
    def merge(l, r):
        return lambda k: l(k) or r(k)

    return reduce(merge, map(dict_pair, updates), base)

###############################################
## "Dictionary" examples
###############################################

me = dict_new(("name", "Alexey"), ("topic", "FP with Python"))
print "Me[name]:", me("name")
print "Me[topic]:", me("topic")
print "Me[nothing]:", me("nothing") # should print None

up = dict_update(me, ("position", "CTO"), ("company", "Kitapps"))
print "Up[name]:", up("name")
print "Up[position]:", up("position")
print "Up[company]:", up("company")


###############################################
## Imitate classes
###############################################

from functools import partial

def ask(self, question):
    return "{name}, {q}?".format(name=self("name"), q=question)

def talk(self):
    return "I'm starting {topic}".format(topic=self("topic"))

def cls(*methods):
    def bind(self):
        return lambda (name, method): (name, partial(method, self))

    return lambda *attrs: dict_new(*(list(attrs) + map(bind(dict_new(*attrs)), methods)))

Speaker = cls(("ask", ask), ("talk", talk))

me = Speaker(("name", "Alexey"), ("topic", "FP with Python"))
print "Me.name:", me("name")
print "Me.topic:", me("topic")
print "Me.talk():", me("talk")()
print "Me.ask(WTF):", me("ask")("WTF")

###############################################
## Output
###############################################

# Me[name]: Alexey
# Me[topic]: FP with Python
# Me[nothing]: None
# Up[name]: Alexey
# Up[position]: CTO
# Up[company]: Kitapps
# Me.name: Alexey
# Me.topic: FP with Python
# Me.talk(): I'm starting FP with Python
# Me.ask(WTF): Alexey, WTF?