symrnn.py

"accumulate repeating characters: convolution frontend, RNN backend"

import collections
from itertools import islice

def conv(iterable, n=2):
    "1d convolution"
    it = iter(iterable)
    window = collections.deque(islice(it, n-1), maxlen=n)
    for x in it:
        window.append(x)
        yield tuple(window)

def forget(h, x):
    "data dependent forget gate of the RNN: updates memory given current input"
    a,b = x
    return h if a == b else ''

def input_projection(x):
    "input projection of the RNN feature"
    a,b = x
    return b

def output_projection(x):
    "output projection of the hidden state"
    return x

def rnn(forget, input, output, xs):
    h = ''
    for x in xs:
        h = forget(h, x) + input(x)
        yield output(h)

input = '_01112233445678'

hidden = conv(input)
for output in rnn(forget, input_projection, output_projection, hidden):
    print(output)