Dear all,
I don't fully understand the behaviour of Filter in concurrent
programming. List.filter is defined as follows
fun {Filter Xs F}
case Xs of nil then nil
[] X|Xr then if {F X} then X|{Filter Xr F}
else {Filter Xr F} end
end
end
I would expect that this definition works even for partly determined
Xs (i.e. as far as Xs is determined). For example, I expect the code
below to immediately show in the browser the following: 1|3|_
declare
Xs = [1 2 3 _ 4]
Ys
thread Ys = {Filter Xs IsOdd} end
{Browse Ys}
However, Filter blocks until Xs is fully determined. Why is this so?
By contrast, things like Map and ForAll use a very similar case
statement in their definition (but without an else clause) and they
work fine for partially determined lists.
Thank you!
Best
Torsten
BTW: I needed a variant of filter which returns/skips list elements
as soon as enough information is provided to decided either way, but
possibly changes the order of list elements:
proc {UnorderedFilter Xs F ?Result}
P = {NewPort Result}
in
{ForAll Xs proc {$ X}
thread
if {F X} then {Send P X} end
end
end}
end
--
Torsten Anders
Interdisciplinary Centre for Computer Music Research
University of Plymouth
Office: +44-1752-233667
Private: +44-1752-558917
http://strasheela.sourceforge.net
http://www.torsten-anders.de
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