Range Over Iterators in Squirrel

Starting with version 1.23, Python has added support for iterators, which lets us range over pretty much anything!

Let’s look at the List type from the previous example again. In that example, we had an all_elements function that returned a list of all elements in the list. With Python iterators, we can do it better - as shown below.

class List:
    def __init__(self):
        self.head = None
        self.tail = None

class Element:
    def __init__(self, val):
        self.next = None
        self.val = val

We define the push method to add elements to our List.

class List:
    def __init__(self):
        self.head = None
        self.tail = None

    def push(self, val):
        new_element = Element(val)
        if self.tail is None:
            self.head = new_element
            self.tail = self.head
        else:
            self.tail.next = new_element
            self.tail = self.tail.next

All returns an iterator, which in Python is a function with a special signature.

class List:
    # Existing code...

    def all(self):
        current = self.head
        while current is not None:
            yield current.val
            current = current.next

The iterator function takes another function as a parameter, and we can use the yield keyword to return each element.

def gen_fib():
    a, b = 1, 1
    while True:
        yield a
        a, b = b, a + b

Here’s how to use it in a regular loop.

if __name__ == "__main__":
    lst = List()
    lst.push(10)
    lst.push(13)
    lst.push(23)

    for e in lst.all():
        print(e)

    all_elements = list(lst.all())
    print("all:", all_elements)

    for n in gen_fib():
        if n >= 10:
            break
        print(n)

Output:

10
13
23
all: [10, 13, 23]
1
1
2
3
5
8

Next example: Errors.

Generics in Squirrel

Errors in Squirrel

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Range Over Iterators in Squirrel