Tcl commands are evaluated if the command name is the first word, at the beginning of a line or when bracketed. eval evaluates its arguments in some special ways (concateneates to a string, if not a pure list). Here are some apocryph alternatives:
Andreas Leitgeb pointed out on the comp.lang.tcl newsgroup (2002-08-07) that
if 1 $cmd
is clearly faster then
eval $cmd
MS explained: "Well: eval does not bytecompile the script as it is "usually" used for one-time scripts ... For more fast-and-surprising ways to do it, try one of
interp eval {} $x
namespace eval :: $xas they both will compile the script."
Tcl chatroom, 2002-12-18:
suchenwi Another wrinkle is that eval does not byte-compile - for that you may use [if 1], [interp eval {}] or [namespace eval ::] ...
EE HOW many different eval commands are there?
dgp YM: [namespace eval [namespace current]]]
suchenwi But such things are not documented features and may change between releases, so don't bet on it. - How many? The four above, and there's also [uplevel 0] ... Don: yes - just quoting MS's hint, assuming that :: is current.
EE eek.
suchenwi Another way:
foreach don't care {#body executed once, but may be left with break}..which you could sugar as:
interp alias {} breakable {} foreach _ _ ...EE ok, there should be a wiki page about how many different ways there are to eval a command. (With discussions of relative merit, of course, and obfuscatory value if you like it that way...)
suchenwi BTW: change the above to:
foreach don't {} {#and the body is not executed, like if 0 }EE yes, I like that. [breakable] looks good.
suchenwi Well I'm not sure whether these really deserve propaganda - it's rather against KISS and all that...
EE really? that doesn't execute the body with don't set to {} ?
suchenwi No - foreach is not executed if the data list is all empty.
miguel foreach eval wayto {gimme $1}
Another special way is a one-off proc if you want to drop local variables immediately:
proc _ {} {#body goes here, may upvar to see the outer world}; _; rename _ {}DGP The comments here are straying off topic. There are indeed many synonyms for [eval] among Tcl's built-in commands, but the last several examples are not among them.