Re: CALC expression feature request

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

Benjamin Franksen wrote:
> It would be very useful if in CALC expressions (e.g. in calc and calcOut 
> record) one could call MIN and MAX with an arbitrary (two or more) number of 
> arguments, instead of only exactly two as it is to date.

I agree that it would, and someone (I forget who) created a version that 
could do that, but that implementation involved pushing a marker 
(probably a NaN) onto the value stack to indicate the start of the 
argument list.  This approach is no longer feasible since the calc 
engine now properly handles NaN and Inf values, so they can't be used as 
markers like that.

Supporting variable length argument lists could mean some fairly 
significant rework on the current base/src/libCom/calc/postfix.c parser, 
although it may not be as hard as I think for someone with a good 
understanding of compilers and parsers.  We do have a fairly good test 
suite for the CALC engine in the libCom/test area now, so this is a 
fairly self-contained work package for anyone who wants to look at it 
(email me first though).

Thanks Ben, I've added this to the list.

- Andrew
--
When a distinguished but elderly scientist states that something is
possible, he is almost certainly right.  When he states that something
is impossible, he is very probably wrong.  -- Arthur C. Clarke