diff options
Diffstat (limited to 'doc/eval.n')
| -rw-r--r-- | doc/eval.n | 25 |
1 files changed, 13 insertions, 12 deletions
@@ -14,7 +14,6 @@ eval \- Evaluate a Tcl script .SH SYNOPSIS \fBeval \fIarg \fR?\fIarg ...\fR? .BE - .SH DESCRIPTION .PP \fBEval\fR takes one or more arguments, which together comprise a Tcl @@ -26,11 +25,13 @@ 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 EXAMPLES +.PP 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, \fBlsort\fR and \fBtrace\fR command callbacks). This example shows how to do this using core Tcl commands: +.PP .CS set script { puts "logging now" @@ -48,35 +49,35 @@ for {set i 0} {$i<10} {incr i} { } .CE .PP -.VS 8.5 Note that in the most common case (where the script fragment is actually just a list of words forming a command prefix), it is better to use \fB{*}$script\fR when doing this sort of invocation 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: +.PP .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] + 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 +.PP However, the last line would now normally be written without \fBeval\fR, like this: +.PP .CS set var [linsert $var 0 {*}$args] .CE -.VE 8.5 - .SH "SEE ALSO" catch(n), concat(n), error(n), interp(n), list(n), namespace(n), subst(n), tclvars(n), uplevel(n) - .SH KEYWORDS concatenate, evaluate, script +'\" Local Variables: +'\" mode: nroff +'\" End: |