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-rw-r--r--doc/eval.n26
1 files changed, 23 insertions, 3 deletions
diff --git a/doc/eval.n b/doc/eval.n
index f027c76..ed46f0c 100644
--- a/doc/eval.n
+++ b/doc/eval.n
@@ -5,7 +5,7 @@
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
-'\" RCS: @(#) $Id: eval.n,v 1.5 2004/05/28 10:37:04 dkf Exp $
+'\" RCS: @(#) $Id: eval.n,v 1.6 2004/10/27 09:36:58 dkf Exp $
'\"
.so man.macros
.TH eval n "" Tcl "Tcl Built-In Commands"
@@ -27,7 +27,7 @@ Tcl interpreter recursively, and returns the result of that
evaluation (or any error generated by it).
Note that the \fBlist\fR command quotes sequences of words in such a
way that they are not further expanded by the \fBeval\fR command.
-.SH EXAMPLE
+.SH EXAMPLES
Often, it is useful to store a fragment of a script in a variable and
execute it later on with extra values appended. This technique is used
in a number of places throughout the Tcl core (e.g. in \fBfcopy\fR,
@@ -46,9 +46,10 @@ for {set i 0} {$i<10} {incr i} {
# Introduce a random delay
after [expr {int(5000 * rand())}]
update ;# Check for the asynch log switch
- eval $script $i [clock clicks]
+ \fBeval\fR $script $i [clock clicks]
}
.CE
+.PP
.VS 8.5
Note that in the most common case (where the script fragment is
actually just a list of words forming a command prefix), it is better
@@ -56,6 +57,25 @@ to use \fB{expand}$script\fR when doing this sort of invokation
pattern. It is less general than the \fBeval\fR command, and hence
easier to make robust in practice.
.VE 8.5
+The following procedure acts in a way that is analogous to the
+\fBlappend\fR command, except it inserts the argument values at the
+start of the list in the variable:
+.CS
+proc lprepend {varName args} {
+ upvar 1 $varName var
+ # Ensure that the variable exists and contains a list
+ lappend var
+ # Now we insert all the arguments in one go
+ set var [\fBeval\fR [list linsert $var 0] $args]
+}
+.CE
+.VS 8.5
+However, the last line would now normally be written without
+\fBeval\fR, like this:
+.CS
+set var [linsert $var 0 {expand}$args]
+.CE
+.VE 8.5
.SH KEYWORDS
concatenate, evaluate, script