A simple iterator protocol for Common Lisp.

com.clearly-useful.iterator-protocol

#+TITLE: simple iterator protocol for common lisp

* com.clearly-useful.iterator-protocol

  *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.

* exported symbols:

** iterator
   /protocol/
   the iterator protocol, which has two methods:
   =iterator-next!= and =iterator-finish!=
   
** iterator
   /type/
   the type of the iterator protocol

** iterator
   /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.

** iterator-p
   /function/
   the test function for the iterator protocol

** iterator-next!
   /protocol method/
   returns two values:
    1. the value of the iterator or nil,
    2. t or nil depending whether a value was found. 
   then advances the iterator.

** iterator-finish!
   /protocol method/
   performs 'clean up' operations specific
   to the iterator. e.g. closing a file.

** do-iterator
   /macro/
   similar to dolist.
   #+begin_src lisp
     (do-iterator (x '(a b c) (list x x))
       (print x))
   #+end_src
   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)
   
   

   


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