OpenEuphoria

Exiting multiple loop constructs

• Posted by Jeremy Cowgar <jeremy at co?gar?com> May 14, 2008
• 1279 views

We've talked about labeled loops and a bit about existing loop constructs,
exiting loops, etc... but I do not think we came to any conclusive decision. Here
is a summary of different methods of exiting multiple loops:

integer in_top
in_top = 1

while in_top do
    for i = 1 to 10 do
        if i = 3 then
            in_top = 0
            exit
        end if
    end for
end while

This will work fine unless you have processing *under* the nested loop, then you
must provide an extra condition check (which is in a loop and is executed each
iteration):

integer in_top
in_top = 1

while in_top do
    for i = 1 to 10 do
        if i = 3 then
            in_top = 0
            exit
        end if
    end for
    if in_top = 0 then
        exit
    end if
    -- do more processing here
end while

NOTE: The above two methods compound in complexity with each nested loop you
add. However, in real life, I'm not sure if I have ever programmed a loop that is
3 deep.

This method uses optional numeric methods to exit and continue keywords:

while 1 do
    for i = 1 to 10 do
        if i = 3 then exit 2 -- end if
    end for
end while

Notice "exit 2". That means exit 2 loops.

The final method is labeled loops, in which I will make a slightly more advanced
example.

while 1 label top do
    for i = 1 to 10 label mid do
        for j = 1 to 10 label bottom do
            -- exit current loop "to" the top loop
            if j = 2 then exit top end if

            -- exit all loops (in this function) 
            if j = 5 then exit all end if
        end for
    end for
end while

So. Is one clearer than another? I do not know. Should any syntax change to
support exiting multiple loops? I am not sure, the benefit is you can remove
multiple checks making code easier to write and better performing.

So, what do you think? Are there other ways that I missed? What should be done?

--
Jeremy Cowgar
http://jeremy.cowgar.com