Re: "continue/next" for "loop"
From: Ole-Hjalmar Kristensen (ole-hjalmar.kristensen_at_substitute_employer_here.com)
Date: 11/03/03
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Date: 03 Nov 2003 14:54:17 +0100
>>>>> "LD" == Lutz Donnerhacke <lutz@iks-jena.de> writes:
LD> * amado.alves wrote:
>>> No. I don't know how to invert a complex loop.
>>
>> What on Earth are you talking about? The two constructs
>>
>> (1) if I mod J = 0 then
>> goto next;
>> end if;
>> Put (I'Img);
>> <<next>> null;
>>
>> (2) if I mod J /= 0 then
>> Put (I'Img);
>> end if;
>>
>> are clearly equivalent!
LD> But both are the result of an oversimplification!
LD> outer: loop
LD> inner: loop
LD> Complex_Actions_1;
LD> if First_Condition then
LD> Some_Justify_Actions;
LD> goto next_outer;
LD> end if;
LD> Complex_Actions_2;
LD> if Second_Condition then
LD> Some_Other_Justify_Actions;
LD> goto next_outer;
LD> end if;
LD> Complex_Actions_3;
LD> end loop inner;
LD> Complex_End_Statments;
LD> exit outer when Other_Condition;
LD> More_Statments;
LD> <<next_outer>> null;
LD> end loop outer;
LD> I'd like to find a more amazing version of this braindead goto.
LD> Please do not assume, that I'm too stupid to invert a condition in a
LD> simplified example. IT'S NOT HOMEWORK!
It seems you are looking for a multi-level "continue" statement :-)
You need to somehow store the results of your tests if you want to
avoid the goto, because this information is used outside the scope of
the inner loop. A boolean should suffice, but is the code any more
readable?
outer: loop
declare
execute_outer_statements : boolean := false;
begin
inner: loop
Complex_Actions_1;
if First_Condition then
Some_Justify_Actions;
else
Complex_Actions_2;
if Second_Condition then
Some_Other_Justify_Actions;
else
Complex_Actions_3;
execute_statements := true;
end if;
end if;
end loop inner;
if execute_outer_statements then
Complex_End_Statments;
exit outer when Other_Condition;
More_Statments;
end if;
end;
end loop outer;
You could of course make your inner loop an inline procedure returning
a boolean to separate the logic of the inner and outer loops more clearly:
outer: loop
declare
procedure inner_loop(doit : out boolean) is
begin
Complex_Actions_1;
if First_Condition then
Some_Justify_Actions;
doit := false;
else
Complex_Actions_2;
if Second_Condition then
Some_Other_Justify_Actions;
doit := false;
else
Complex_Actions_3;
doit := true;
end if;
end if;
end inner_loop;
pragma inline(inner_loop);
execute_outer_statements : boolean;
begin
inner_loop(execute_outer_statements);
if execute_outer_statements then
Complex_End_Statments;
exit outer when Other_Condition;
More_Statments;
end if;
end;
end loop outer;
After looking at these alternatives, I would probably stick with the goto.
-- Strange attractors stole my wife
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