generators

2013-06-15

Generators

Generators is a library that provides python style generators in common lisp, by using cl-cont delimited continuations

This library is more of an interesting toy, though as far as I know it does work. I dont think I have ever used this in application code, though I think that with care, it could be.

Requirements

  • CL-CONT provides the continuations that make this work
  • Alexandria
  • Iterate

Gotchas

  • Continuations don't play nicely with exception/signal handling, unwind-protect, throw/catch, or dynamic variables. Consider using cl-cont:without-call/cc, if you need this functionality in a generator. (see-also %mv-gen for an example)

  • because cl-cont uses a code walker, it might get confused when interacting other code walkers (eg: iterate). Inside of generators, you might have better luck with less code walking

API

make-generator

Creates a new generator, the body of which can yield values to the calling scope

yield

yield - returns the next value from the generator to the caller

yielding

yielding - yields every value in the passed in generators

Iterate clauses

(for v in-generator gen)

iterates through the values produced by a generator

(FOR node a-node-of-lisp-tree tree)

iterates through all the nodes of a lisp tree eg: '(1 (2 3) 4) generates (1 (2 3) 2 3 4)

(FOR node a-leaf-of-lisp-tree tree)

iterates through all the leaves of a lisp tree eg: '(1 (2 3) 4) generates (1 2 3 4)

Example:

(defun generate-lisp-tree-nodes (trees &optional leaves-only?)
  "Do a depth first traversal of some set of trees yielding every node/leaf "
  (make-generator ()
    (iter (for n in (alexandria:ensure-list trees))
      (etypecase n
        (atom (yield n))
        (list
         (unless leaves-only? (yield n))
         (yielding (generate-lisp-tree-nodes n)))))))

Authors

;; Copyright (c) 2013 Russ Tyndall , Acceleration.net http://www.acceleration.net
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Author
<programmers@acceleration.net>
License
BSD
Categories
accelerationnet, continuations, language extension, python