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 $cmdis clearly faster then eval $cmdSee [Many ways to eval] for the ensuing discussion.
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."