Re: Unbalanced conditional ?

[Andrew Johnson <anj@aps.anl.gov>]

Hi Dirk,

On 2011-12-08 Dirk Zimoch wrote:
> > When I tried to upgrade from 3.14.8 to 3.14.12, I found that some CALC
> > expressions are not working any more, e.g. "B=0?A"
> >
> > In 3.14.8 and all previous versions that meant: If B is 0 then set VAL
> > to A otherwise don't change VAL.
> >
> > Now, I get the error message:
> >
> > Unbalanced conditional ?: operators in CALC expression 'B=0?A'
> > Can't set "recordname.CALC" to "B=0?A"
> >
> > Was there any good reason for this incompatible change in the CALC
> > behavior?

Yes, it was really obscure; I didn't know it worked at the time, let alone 
that it was documented.  There was certainly nothing in the code to indicate 
that it was meant to be legal.

You can add ":VAL" to fix old expressions, which in 3.14.12 and later can be 
up to 79 characters long.

> The change is not mentioned in the release notes
> http://www.aps.anl.gov/epics/base/R3-14/12-docs/RELEASE_NOTES.html

> Thus I guess the new behavior was not intended and is a bug.

The change was part of a major rewrite of the CALC expression parser that was 
released as part of 3.14.9 in 2007.  Making this legal again would IMHO be a 
backwards step since there is an easy fix for old expressions and the results 
are easier to understand.

Sorry, that's just another change you'll have to make when upgrading.

- Andrew
-- 
Optimization is the process of taking something that works and
replacing it with something that almost works, but costs less.
-- Roger Needham