Question

So Ive been giving the following code in a kind of sort of python class. Its really a discrete math class but he uses python to demonstrate everything. This code is supposed to demonstate a multiplexer and building a xor gate with it.

def mux41(i0,i1,i2,i3):
    return lambda s1,s0:{(0,0):i0,(0,1):i1,(1,0):i2,(1,1):i3}[(s1,s0)]

def xor2(a,b):
    return mux41(0,1,1,0)(a,b)

In the xor2 function I dont understand the syntax behind return mux41(0,1,1,0)(a,b) the 1’s and 0’s are the input to the mux function, but what is the (a,b) doing?

Answer 1

The (a, b) is actually the input to the lambda function that you return in the mux41 function.

Your mux41 function returns a lambda function which looks like it returns a value in a dictionary based on the input to the mux41 function. You need the second input to say which value you want to return.

It is directly equivalent to:

def xor2(a,b):
    f = mux41(0,1,1,0)
    return f(a,b)