CL-COROUTINE is a coroutine library for Common Lisp. It uses CL-CONT continuations library in its implementation.

Coroutines can be defined using defcoroutine macro.

To use defined coroutines, first create a coroutine object with calling make-coroutine function, then just funcall to process it.

yield macro control back to the context which called the coroutine and the coroutine will resume processing at this point when it will be called again.

;; define a coroutine using DEFCOROUTINE macro
(defcoroutine example (whom)
  (format t "First greeting to: ~A~%" whom)
  (yield 1)
  (format t "Second greeting to: ~A~%" whom)
  (yield 2)
  (format t "Third greeting to: ~A~%" whom)
  (coexit 3)
  (format t "No greeting to: ~A~%" whom)
  (yield 4))
=> EXAMPLE

;; make a coroutine object
(setf coroutine (make-coroutine 'example))
=> a coroutine object

;; funcall it
(funcall coroutine "Smith")
>> First greeting to: Smith
=> 1

;; funcall again
(funcall coroutine "Johnson")
>> Second greeting to: Johnson
=> 2

;; funcall again and coexit
(funcall coroutine "Williams")
>> Third greeting to: Williams
=> 3

;; funcall after coexit just returns no value
(funcall coroutine "Brown")
=> No value

;; you can also use WITH-COROUTINE macro to set up coroutines,
;; which provides calling coroutines without explicit FUNCALL
(with-coroutine (example)
  (example "Smith")
  (example "Johnson"))
>> First greeting to: Smith
>> Second greeting to: Johnson
=> 2

You can install cl-coroutine via Quicklisp:

(ql:quickload :cl-coroutine)

CL-COROUTINE has some restrictions because of its dependency on CL-CONT library.

• special forms that CL-CONT library does not support with CALL/CC
• coroutines with very long definition might need much time to compile

DEFCOROUTINE coroutine-name arg &body body => coroutine-name

Defines a new coroutine named coroutine-name that has atmost one argument as arg. The definition of coroutine is stored in the property list of coroutine-name symbol. Defined coroutines will be created using make-coroutine function.

YIELD [result] => |

Yields control back to the context which called the coroutine, passing along any multiple values that were passed to it. The coroutine will resume processing at this point when it will be called again. Any arguments passed to the next calling will be set to the coroutine's corresponding parameters implicitly.

COEXIT [result] => |

Returns control to the context which called the coroutine, passing along any multiple values that were passed to it. The difference from yield macro is that the coroutine will never resume processing at this point anymore. If the coroutine will be called again, it will just return no value.

MAKE-COROUTINE coroutine-name => coroutine

Creates and returns a coroutine corresponding to coroutine-name. The returned coroutine can be called with funcall or apply functions.

WITH-COROUTINE (coroutine-name) &body body => results

with-coroutine uses make-coroutine to create a coroutine with name coroutine-name and defines a local macro with name coroutine-name binding it with the coroutine. with-coroutine evaluates the body as an implicit progn with the macro.

• Masayuki Takagi ([email protected])

Copyright (c) 2014 Masayuki Takagi ([email protected])

Licensed under the LLGPL License.