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Diffstat (limited to 'doc/eval.n')
| -rw-r--r-- | doc/eval.n | 45 |
1 files changed, 15 insertions, 30 deletions
@@ -4,7 +4,7 @@ '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. -'\" +'\" .TH eval n "" Tcl "Tcl Built-In Commands" .so man.macros .BS @@ -14,6 +14,7 @@ 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 @@ -23,22 +24,13 @@ fashion as the \fBconcat\fR command, passes the concatenated string to the 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; -for \fIany\fR values, $a, $b, and $c, these two lines are effectively -equivalent: -.PP -.CS -\fBeval\fR [list $a $b $c] -$a $b $c -.CE +way that they are not further expanded by the \fBeval\fR command. .SH EXAMPLES -.PP Often, it is useful to store a fragment of a script in a variable and execute it later on with extra values appended. This technique is used in a number of places throughout the Tcl core (e.g. in \fBfcopy\fR, \fBlsort\fR and \fBtrace\fR command callbacks). This example shows how to do this using core Tcl commands: -.PP .CS set script { puts "logging now" @@ -56,42 +48,35 @@ for {set i 0} {$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 -.PP +.VS 8.5 However, the last line would now normally be written without \fBeval\fR, like this: -.PP .CS set var [linsert $var 0 {*}$args] .CE -.PP -or indeed like this: -.PP -.CS -set var [list {*}$args {*}$var] -.CE +.VE 8.5 + .SH "SEE ALSO" -catch(n), concat(n), error(n), errorCode(n), errorInfo(n), interp(n), list(n), -namespace(n), subst(n), uplevel(n) +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: |