See Tcl shell code & results below:
% foreach a { 1 2 3 4 5 } { puts $a }
1
2
3
4
5
% puts $a
5
It would appear that variable a stays in the memory... In Perl, for example one can use:
foreach my $a
And have $a exist just during the looping. in Ruby, one can use closures:
[1,2,3,4,5].each{|a| puts a.to_s() }
In order to achieve the same.
Is there an elegant way to this in Tcl?
Thanks
You can iterate within a closure:
apply {vals {foreach a $vals {puts $a}}} {1 2 3 4 5}
alternatively you can make the body a parameter (in which case the looping variable’s name should be a parameter too):
apply {{varName vals body} {foreach $varName $vals $body}} a {1 2 3 4 5} {puts $a}
If you call this myForeach or something, it looks less cumbersome:
set myForeach {{varName vals body} {foreach $varName $vals $body}}
apply $myForeach a {1 2 3 4 5} {puts $a}
You can also make this an interpreter macro:
set myForeach {{varName vals body} {foreach $varName $vals $body}}
interp alias {} myForeach {} apply $myForeach
myForeach a {1 2 3 4 5} {puts $a}
Documentation: apply, foreach, interp package, interp, puts, set
This is not the current semantics of foreach, and this is extremely unlikely to change in the near future as it would have a severe impact on many people's existing code. In particular, many people currently use:
foreach {a b c d} $someList break
Instead of doing:
lassign $someList a b c d
Because that was what worked in Tcl 8.4 and before and they've not updated their coding style since.
unsetcommand to achieve the same after theforeachloop.foreachcommand's behavior withrenameand do theunsetoperation for you.