6.9.4 Begin loops with multiple exits

For counted loops, you can use leave in several places. For begin loops, you have the following options:

Use exit (possibly several times) in the loop to leave not just the loop, but the whole colon definition. E.g.,:

     : foo
       begin
         condition1 while
           condition2 if
             exit-code2 exit then
           condition3 if
             exit-code3 exit then
         ...
       repeat
       exit-code1 ;

The disadvantage of this approach is that, if you want to have some common code afterwards, you either have to wrap foo in another word that contains the common code, or you have to call the common code several times, from each exit-code.

Another approach is to use several whiles in a begin loop. You have to append a then behind the loop for every additional while. E.g.,;

     begin
       condition1 while
         condition2 while
           condition3 while
     again then then then

Here I used again at the end of the loop so that I would have a then for each while; repeat would result in one less then, but otherwise the same behaviour. For an explanation of why this works, See Arbitrary control structures.

We can have common code afterwards, but, as presented above, we cannot have different exit-codes for the different exits. You can have these different exit-codes, as follows:

     begin
       condition1 while
         condition2 while
           condition3 while
     again then exit-code3
     else exit-code2 then
     else exit-code1 then

This is relatively hard to comprehend, because the exit-codes are relatively far from the exit conditions (it does not help that we are not used to such control structures, either).