| Re: Recursion in IDL [message #877 is a reply to message #873] |
Mon, 05 April 1993 10:24  |
alans
Messages: 12
Registered: September 1991
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Junior Member |
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Recursion only works on procedures, though. It would be far more useful
for IDL to support recursive *functions*. Unfortunately, this is more
difficult for IDL's parser, I guess, because it has to distinguish between a
function call and an array subscript operation which share the same syntax.
E.G.,
function foo, bar
if (bar eq 1) then $
return, 1 else $
return, bar * foo (bar-1)
end
IDL> print,foo(2)
% Variable is undefined: FOO.
% Execution halted at FOO </dev/tty( 1)> .
% Called from FOO </dev/tty( 2)>.
% Called from $MAIN$ .
Yecch! Does anyone know a way around this? Compile it twice? (Yes,
actually I just tried and it *does* work if you ".run" it twice. (*WOW*) So
I take it all back; IDL *does* support recursive functions, albeit with an
ugly hack. For the record, I'm running IDL 3.0.0 on Sparc SunOs 4.1.1...
RSI, I understand the difficulty involved, but can something be done about
that? I never explicitly ".run" anything; I put all procedures & functions
in my IDL path, and have encouraged my colleagues to do the same...Gee,
think of the CPU-hogging Object-Oriented possibilities with this - functions
which walk structures of structures looking for a particular field names,
recursive "sizeof"-type operations, etc. It boggles the imagination! ;-)
--
Alan J.Stein MIT/Lincoln Laboratory alans@ll.mit.edu
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