Slice API for lists

It implements a slice API allowing you to emulate the Python index notation in Erlang and Elixir. It's made of the following two functions.

• slice:index/2
• slice:range/2

Consider a list like ['a', 'b', 'c', 'd', 'e'] in Python. With its index notation you can easily retrieve the last element, the last three elements, or let's say, the whole list without the first and last element.

l = ['a', 'b', 'c', 'd', 'e']
print(l[-1])   # 'e'
print(l[-3:])  # ['c', 'd', 'e']
print(l[1:-1]) # ['b', 'c', 'd']

With the slice API, you can easily compute those elements and sub-lists using the same values.

Getting started

Let's consider the very same list in Erlang.

List = [a, b, c, d, e].

To compute a single element, use the slice:index/2 function. For instance, here is how to compute the last element.

Index = slice:index(length(List), -1).
e = lists:nth(List, Index).

The slice:index/2 function uses a 0-based index and returns the value that must be passed to the lists:nth/2 function to compute the element.

To compute a sub-list, use the slice:range/2 function. For instance, here is how to compute the last 3 elements, and the whole list without the first and last element.

{Start, Length} = slice:range(length(List), {-3, undefined}).
[c, d, e] = lists:sublist(List, Start, Length).

{Start, Length} = slice:range(length(List), {1, -1}).
[b, c, d] = lists:sublist(List, Start, Length).

The slice:range/2 function uses 0-based indexes and returns the values that must be passed to the lists:sublist/3 function to compute the sub-list.

It's essentially just that. For the details of the API, refer to the documentation for more information.