Overview: This package provides a simple iterator protocol for common lisp which integrates with the sequence protocol.
From the protocol docstring:
A simple iteration protocol for Common Lisp. Unlike sequences, iterators are stateful, and are not intended to be held onto or passed around. Their use should be hidden by some other construct. If you are explicitly creating and advancing an iterator, chances are you are Doing It Wrong. Iterators should be be treated as though they have dynamic extent.
This package is intentionally minimal, and only provides a protcol for handling stateful iterators & basic implementations for built in types. This protocol e.g. consume an object representing the lines of a file, or some strings in memory, without having to special case anything. The actual implementation of such an object is beyond the scope of this package.
protocol
the iterator protocol, which has two methods:
iterator-next! and iterator-finish!
type the type of the iterator protocol
generic function
a function to produce an iterator from an object.
this function acts as the identity function for
iterators, and provides a default implementation
for the built in types vector and array, as
well as any object implementing the seq protocol.
function the test function for the iterator protocol
protocol method returns two values:
- the value of the iterator or nil,
- t or nil depending whether a value was found.
then advances the iterator.
protocol method performs ‘clean up’ operations specific to the iterator. e.g. closing a file.
macro similar to dolist.
(do-iterator (x '(a b c) (list x x))
(print x))will call iterator on ‘(a b c), bind x to subsequent values of iterator-next!, finally call iterator-finish! and return the value of (list x x), i.e. print a, b, and c, then return ‘(c c)