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evaluation of logical expressions [message #5083]

Thu, 21 September 1995 00:00

Russ Welti
Messages: 27
Registered: October 1994

Junior Member

I've often wondered the reason why the following:

IDL> a=0
IDL> if a and b then print,'yes'
% Variable is undefined: B.
% Execution halted at: $MAIN$

Many languages stop evaluating logical expressions as soon
as the result can be determined. I'm sure there's a good
reason why IDL doesn't, but it means that in my code I
use a lot of these:

if n_elements(a) GT 0 then $
if a EQ 5 then $

where I *would* have liked to say:

if n_elements(a) GT 0 and a EQ 5 then $

Anybody know any background on this?
/
Russ Welti /-\
rwelti@u.washington.edu \-/

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