Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Fri, 09 Dec 2011 17:55:28 +0100

I did some tests with the ?: syntax.

Even though unbalanced ?: are generally not valid, unbalanced

sub-expressions are accepted and do interesting things.

"(A?B):C" and "A?(B:C)" are accepted and work like "A?B:C"
"SIN(A?B):C" is accepted and works like "A?SIN(B):C"
"A?SIN(B:C)" is accepted and works like "SIN(A?B:C)"

You can add ":VAL" to fix old expressions

That has not exactly the same effect. The old syntax "A?B" raised a

CALC/INVALID alarm when A is false. The INVALID can be checked for with

IVOA and can be passed to other records with MS links. I do not see a

full replacement for this behavior.

Dirk

Andrew Johnson wrote:

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

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System