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INFO-DIR-SECTION The Algorithmic Language Scheme
START-INFO-DIR-ENTRY
* generator.egg: (generator.egg).		Provides generator-like coroutine operations.
END-INFO-DIR-ENTRY


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generator egg
*************

Provides generator-like coroutine operations.

Written by Kon Lovett (mailto:klovett@pacbell.net)

   This manual corresponds to version 1.1 of the generator extension
library for Chicken Scheme.

* Menu:

* About this egg::
* Documentation::
* Examples::
* License::
* Index::


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1 About this egg
****************

* Menu:

* Version history::
* Usage::


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1.1 Version history
===================

`1.1'
     Added generator procedure

`1.0'
     Initial release


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1.2 Usage
=========

Load this egg like so:

   `(require-extension generator)'


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2 Documentation
***************

generator is a set of routines supporting generator-like operations.

 -- macro: coroutine
          (coroutine ARG EXPR ...)

     Returns a coroutine procedure of one argument.  					Use '(resume
     COROUTINE VALUE)' within the body to 					invoke another
     coroutine.

 -- macro: define-generator
          (define-generator (NAME ARG ...) EXPR ...)

     Defines a procedure, `NAME', that, when 					invoked, returns a
     generator parameterized on '`ARG ...''. The '(yield VALUE)'
     procedure is 					used within the body '`EXPR ...'' of the
     generator to produce a single value. Multi-valued 					yield is not
     supported.

 -- procedure: make-generator
          (make-generator ROUTINE [SENTINEL])

     Returns a generator procedure, of zero or one argument.

     `ROUTINE' is a procedure of one argument, invoked 					with the
     generator "yield value" procedure. The 					yield procedure
     takes one argument, the "next 					value".

     `SENTINEL' is a value to return, or a zero-argument
     procedure to call, when the generator becomes 					'dead', otherwise
     continues at caller parent.

     The generator procedure argument may be:

     none - invokes the routine `ROUTINE' 					with "yield value"
     procedure

     'status - returns the generator run status, 'dead or 'alive

     'dead? - queries whether generator is not runnable

     'alive? - queries whether generator is runnable

     'kill! - makes the generator not runnable

 -- procedure: generator
          (generator PROC-OF-YIELDER [SENTINEL])

     Takes a one argument procedure to generate. Invokes the
     generating procedure with the 'yield' procedure as the
     argument. The generating procedure calls the yield procedure 					to
     produce a value. The generator terminates when the
     generating procedure exits without invoking yield.

     When the `SENTINEL' is missing 'end-of-generator 					is used.


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3 Examples
**********


(use generator)

(define (list->iterator ls) (make-generator (lambda (yield) (for-each yield ls))))

(define (iterator-empty? lsi) (lsi 'dead?))

(define t (list->iterator '(1)))
(t)		# 1; continues at caller
(t)		# nothing; continues at caller parent
(t)		# Error: (generator) dead

(define t (list->iterator '(1 2)))
(t)		# 1; continues at caller
(t 'kill!)	# dead
(t)		# Error: (generator) dead

(define-generator (counter n) (yield n) (counter (add1 n)))
(define t (counter 20))
(t)	# 20
(t)	# 21
...and so on

(define (gen-list lst)
  (generator
    (lambda (yield)
      (let loop ([lst lst])
        (when (pair? lst)
           (yield (car lst))
           (loop (cdr lst)))))))

> (define gen (gen-list '(a b c)))
> (gen)
a
> (gen)
b
> (gen)
c
> (gen)
end-of-generator


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4 License
*********


Copyright (c) 2005, Kon Lovett.  All rights reserved.

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the Software),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ASIS, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.


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Index
*****

 [index ]
* Menu:

* coroutine:                             Documentation.        (line  9)
* define-generator:                      Documentation.        (line 16)
* generator:                             Documentation.        (line 51)
* make-generator:                        Documentation.        (line 25)



Tag Table:
Node: Top258
Node: About this egg641
Node: Version history811
Node: Usage1005
Node: Documentation1173
Node: Examples3246
Node: License4142
Node: Index5323

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