'''[http://www.tcl.tk/man/tcl/tclcmd/continue.htm%|%continue]''', a [tcl
commands%|%built-in] tcl command, skips to the next iteration of a loop
** see also **
[break]:
[breakeval]:
[return]:
** loop commands **
[for]:
[foreach]:
[while]:
** documentation **
[http://www.tcl.tk/man/tcl8.5/tclcmd/continue.htm%|%official reference]:
** synopsis **
'''continue'''
** description **
this command is typically invoked inside the body of a looping command such as
for or foreach or while. it returns a tcl_continue code, which causes a
continue exception to occur. the exception causes the current script to be
aborted out to the innermost containing loop command, which then continues with
the next iteration of the loop. catch exceptions are also handled in a few
other situations, such as the catch command and the outermost scripts of
procedure bodies.
** examples **
print a line for each of the integers from 0 to 10 except 5:
======
for {set x 0} {$x<10} {incr x} {
if {$x == 5} {
continue
}
puts "x is $x"
}
======
** discussion **
[les]: suppose the following code:
======
foreach i $list1 {
foreach j $list2 {
if [some condition] {continue}
eval {blah blah blah}
}
}
======
[[`continue`] interrupts the [[`[foreach]`] `j` loop. but what if i wanted it
to break the foreach `i` loop?
place [[`[foreach] i]`] in a proc and use [[`[return]`] instead of
[[`[continue]`].
[lars h]: or use [breakeval] as follows
======
foreach i $list1 {
breakeval-aware foreach j $list2 {
if {[some condition]} then {
breakeval {continue} ; # break out of j loop, do a continue for the i loop.
}
eval {blah blah blah}
}
}
======
[mg] 2005-04-20: in [php], ''continue'' (and ''break'') accept an argument that
tells it how many nesting levels to continue/break for, slightly-similar to
return's -code option. how hard would it be to add something like that into
tcl? since neither [break] nor [continue] accept any arguments right now, as
long as it defaulted to 1 it would have total backwards-compatability, and
would, imho, be more "natural" than the above.
[schlenk]: did you try [[`[return]` -code continue -level ...]
''[lars h]: that won't work, because it wouldn't become a continue until it
returns from some proc.''
[les]: these suggestions all involve creating yet another proc for my code,
which is not really what i was looking for. i was indeed thinking of [php]'s
continue/break argument, as [mg] mentioned. i asked the question in the first
place because i already have a solution, but it forces me to add more code to
an already very long proc that i am trying to do some liposuction on. some sort
of "loop depth argument" would help me make it shorter. anyway, here is my
current solution:
======
foreach i $list1 {
set _break 0
foreach j $list2 {
if {[some condition]} {
incr _break
break
}
eval {blah blah blah}
}
if {$_break > 0} continue
...
}
======
conclusion: if you come from [php], now you know that there is no
continue/break "loop depth argument". but several workarounds are offered above
(and below?).
----
[PYK]: another kind of sugar:
======
foreach i $list1 {
set continue list
foreach j $list2 {
if {[some condition]} {
set continue continue
break
}
eval {blah blah blah}
}
$continue
...
}
======
----
[lv]: given that there's already the weird return arguments, what is the
argument against enhancing continue as described above? is there a technical
issue with the proposal?
[rhs]: the idea of enhancing break and continue to accept an optional ''depth''
argument has been brought up multiple times in the past. i've never seen a
counter-argument as to why it would be a bad idea... i've never seen anyone
with enough motivation to even write up a tip for it either, though. i've had
cases where i'd like to have had the feature, and i'm too lazy to write a tip
for it, so i can't really complain that someone else hasn't either.
[escargo] 2005-04-20: in [Icon Programming Language%|%icon], ''break'' and
'''next''' (the equivalent of
continue) both have optional expressions that are
evaluated in the context
outside the current loop. so, if you are in inner
loop and you want to leave
that one loop, you use '''break'''. if you want to
leave both an inner and
outer loop, you would use '''break break'''.
[lars h]: there is such an rfe logged for tcl
[http://sourceforge.net/tracker/index.php?func=detail&aid=550789&group_id=10894&atid=360894].
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