Chapter 7: Adding Variables to S-Calc

Variable Scope

Consider the following variables, and the function $f$.



In [11]:

    
x = 1
y = 2
def f():
    x = 3
    y = 4

What will happen when we call the function $f$... what will the values of x and y be after the function call?



In [12]:

    
f()
print(x, y)

1 2

So, how many variables are there?

Closures

To explore more complex variable bindings, we introduce the idea of a closure. A closure is a fuction that captures the bindings of variables.



In [19]:

    
x = 1
y = 2
def make_closure():
    x = 3
    y = 4
    def f():
        print(x, y)
    return f



In [20]:

    
c = make_closure()
c()

3 4



In [22]:

    
x, y









    Out[22]:





(1, 2)



In [23]:

    
c()

3 4



In [1]:

    
x = 5
y = 13
def make_closure():
    x = 42
    y = 911
    def func():
        global x # sees the global value
        print(x, y)
        x += 1

    return func



In [ ]:

    
def make_closure():
    value = 0
    def get_next_value():
        nonlocal value
        value += 1
        return value
    return get_next_value