(Thanks for changing the Subject:)
On Tue, 24 Mar 2020 11:19:16 -0400, Bob Bridges wrote:
>There is such a thing as overdoing GOTOs, but I agree that a blanket
>never-do-it rule is counter-productive. I don't often use SIGNAL in REXX,
>because I find that its structured features are adequate. But in other
>languages I have argued for limited GOTO use.
>
>In COBOL, for example, it seems to me that there's a place for GOTO
>TOP-OF-PARAGRAPH (to simulate ITERATE in REXX), GOTO EXIT-PARAGRAPH (to
>simulate LEAVE) and GOTO END-OF-PROGRAM (for controlled abend conditions).
>These don't violate structured-programming principles, they implement them.
>In VBA I freely use Goto IterateSomething (putting the label just before the
>Next statement). I don't think PL/1 ever needs it, but I'm glad it's there
>just in case.
>
>Even in REXX there's one missing structured ingredient: some way to leave a
>~simple~ block. A SELECT comes close, but it's not perfect. Say you're
>looping through a list of candidates and have to perform a number of
>candidates:
>
> do jr=1 to stem.0
> v0=stem.jr
> if v0='' then iterate
> v1=function1(v0)
> if v1<5 then iterate
> v2=functionv2(v1 + othervalue)
> if v2=previous then iterate
> say 'TRK:' v0 v1 v2
> end
>
I almost always label ITERATE, LEAVE, and END for clarity and'
syntax error detection:
do jr=1 to stem.0
v0=stem.jr
if v0='' then iterate jr
v1=function1(v0)
if v1<5 then iterate jr
v2=functionv2(v1 + othervalue)
if v2=previous then iterate jr
say 'TRK:' v0 v1 v2
end jr
(Even though it looks more like "GOTO jr".)
>That's great in a controled DO loop. But it's harder in simple block of code.
> A SELECT won't do the job, because of the calculations you have to do between
>the various tests. I handle it this way:
>
> do 1
> if v0='' then leave
> v1=function1(v0)
> if v1<5 then leave
> v2=functionv2(v1+othervalue)
> if v2=previous then leave
> say 'TRK:' v0 v1 v2
> end
>
Even at the cost of introducing an almost-otiose control variable:
do myBlock= 0 for 1
if v0='' then leave myBlock
v1=function1(v0)
if v1<5 then leave myBlock
v2=functionv2(v1+othervalue)
if v2=previous then leave myBlock
say 'TRK:' v0 v1 v2
end myBlock
>I always suspect I'd get complaints from structured enthusiasts if they ever
>saw me cheating like that. ...
>
Not from me. Except for not using labels.
-- gil
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