Revision 07fc868ecfd31fecc7c3f964730f946c31f5ab80 authored by Joshua J. Cogliati on 19 June 2020, 15:11:03 UTC, committed by Joshua J. Cogliati on 19 June 2020, 15:11:03 UTC
1 parent ecd99ed
dmaybeoutput
.MAYBEOUTPUT value (special form)
works like OUTPUT except that the expression that provides the
input value might not, in fact, output a value, in which case
the effect is like STOP. This is intended for use in control
structure definitions, for cases in which you don't know whether
or not some expression produces a value. Example:
to invoke :function [:inputs] 2
.maybeoutput apply :function :inputs
end
? (invoke "print "a "b "c)
a b c
? print (invoke "word "a "b "c)
abc
This is an alternative to RUNRESULT. It's fast and easy to use,
at the cost of being an exception to Logo's evaluation rules.
(Ordinarily, it should be an error if the expression that's
supposed to provide an input to something doesn't have a value.)
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