diff options
Diffstat (limited to 'contrib/tcl/doc/while.n')
| -rw-r--r-- | contrib/tcl/doc/while.n | 24 |
1 files changed, 21 insertions, 3 deletions
diff --git a/contrib/tcl/doc/while.n b/contrib/tcl/doc/while.n index 8703684d518b6..326d18f76e65f 100644 --- a/contrib/tcl/doc/while.n +++ b/contrib/tcl/doc/while.n @@ -1,11 +1,11 @@ '\" '\" Copyright (c) 1993 The Regents of the University of California. -'\" Copyright (c) 1994-1996 Sun Microsystems, Inc. +'\" Copyright (c) 1994-1997 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" SCCS: @(#) while.n 1.6 96/03/25 20:27:35 +'\" SCCS: @(#) while.n 1.7 97/04/08 17:13:50 '\" .so man.macros .TH while n "" Tcl "Tcl Built-In Commands" @@ -19,7 +19,7 @@ while \- Execute script repeatedly as long as a condition is met .SH DESCRIPTION .PP -The \fIwhile\fR command evaluates \fItest\fR as an expression +The \fBwhile\fR command evaluates \fItest\fR as an expression (in the same way that \fBexpr\fR evaluates its argument). The value of the expression must a proper boolean value; if it is a true value @@ -32,6 +32,24 @@ iteration of the loop, and \fBbreak\fR commands may be executed inside \fIbody\fR to cause immediate termination of the \fBwhile\fR command. The \fBwhile\fR command always returns an empty string. +.PP +Note: \fItest\fR should almost always be enclosed in braces. If not, +variable substitutions will be made before the \fBwhile\fR +command starts executing, which means that variable changes +made by the loop body will not be considered in the expression. +This is likely to result in an infinite loop. If \fItest\fR is +enclosed in braces, variable substitutions are delayed until the +expression is evaluated (before +each loop iteration), so changes in the variables will be visible. +For an example, try the following script with and without the braces +around \fB$x<10\fR: +.CS +set x 0 +while {$x<10} { + puts "x is $x" + incr x +} +.CE .SH KEYWORDS boolean value, loop, test, while |