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diff --git a/doc/coroutine.n b/doc/coroutine.n new file mode 100644 index 0000000..ad9fddd --- /dev/null +++ b/doc/coroutine.n @@ -0,0 +1,108 @@ +'\" +'\" Copyright (c) 2009 Donal K. Fellows. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +'\" RCS: @(#) $Id: coroutine.n,v 1.1 2009/03/25 10:26:11 dkf Exp $ +'\" +.so man.macros +.TH coroutine n 8.6 Tcl "Tcl Built-In Commands" +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +coroutine, yield \- Create and produce values from coroutines +.SH SYNOPSIS +.nf +\fBcoroutine \fIname command\fR ?\fIarg...\fR? +\fByield\fR ?\fIvalue\fR? +\fIname\fR ?\fIvalue\fR? +.fi +.BE +.SH DESCRIPTION +.PP +The \fBcoroutine\fR command creates a new coroutine context (with associated +command) named \fIname\fR and executes that context by calling \fIcommand\fR, +passing in the other remaining arguments without further interpretation. Once +\fIcommand\fR returns normally or with an exception (e.g., an error) the +coroutine context \fIname\fR is deleted. +.PP +Within the context, values may be generated as results by using the +\fByield\fR command; if no \fIvalue\fR is supplied, the empty string is used. +When that is called, the context will suspend execution and the +\fBcoroutine\fR command will return the argument to \fByield\fR. The execution +of the context can then be resumed by calling the context command, optionally +passing in the value to use as the result of the \fByield\fR call that caused +the context to be suspended. If the coroutine context never yields and instead +returns conventionally, the result of the \fBcoroutine\fR command will be the +result of the evaluation of the context. +.PP +The coroutine can also be deleted by destroying the command \fIname\fR, and +the name of the current coroutine can be retrieved by using \fBinfo +coroutine\fR. If there are deletion traces on variables in the coroutine's +implementation, they will fire at the point when the coroutine is explicitly +deleted (or, naturally, if the command returns conventionally). +.SH EXAMPLES +.PP +This example shows a coroutine that will produce an infinite sequence of +even values, and a loop that consumes the first ten of them. +.PP +.CS +proc allNumbers {} { + \fByield\fR + set i 0 + while 1 { + \fByield\fR $i + incr i 2 + } +} +\fBcoroutine\fR nextNumber allNumbers +for {set i 0} {$i < 10} {incr i} { + puts "received [\fInextNumber\fR]" +} +rename nextNumber {} +.CE +.PP +In this example, the coroutine acts to add up the arguments passed to it. +.PP +.CS +\fBcoroutine\fR accumulator apply {{} { + set x 0 + while 1 { + incr x [\fByield\fR $x] + } +}} +for {set i 0} {$i < 10} {incr i} { + puts "$i -> [\fIaccumulator\fR $i]" +} +.CE +.PP +This example demonstrates the use of coroutines to implement the classic Sieve +of Eratosthenes algorithm for finding prime numbers. +.PP +.CS +proc filterByFactor {source n} { + \fByield\fR [info coroutine] + while 1 { + set x [$source] + if {$x % $n} { + \fByield\fR $x + } + } +} +\fBcoroutine\fR allNumbers apply {{} {while 1 {\fByield\fR [incr x]}}} +set c allNumbers +for {set i 1} {$i <= 20} {incr i} { + set n [$c] + puts "prime#$i = $n" + set c [\fBcoroutine\fR prime$i filterByFactor $c $n] +} +.CE +.SH "SEE ALSO" +apply(n), info(n), proc(n), return(n) +.SH KEYWORDS +coroutine, generator +'\" Local Variables: +'\" mode: nroff +'\" fill-column: 78 +'\" End: |