Stefan Scott Alexx wrote:
> So I am curious whether J has mechanisms similar to K's dependencies and
> triggers.
Nope. We do have memory mapped files which update "everywhere" (including
across processes) simultaneously, but you aren't
"notified" of this (the global just always has the "correct", current value) .
> Alternatively, (if J lacks such mechanisms) I would be very appreciative for
> any ideas
> on how to go about simulating K's dependencies and triggers in J.
This really depends on what triggers these changes. If it's just code that
assigns a global in K, then in J instead of the
assignment statement, you could call a function (verb) which updates the global
and all its relatives. This verb would be
semantically similar to the "dependency" statements you mentioned in K.
If it's some external event, like a user clicking a button or a request coming
in on a socket, or a certain amount of time passing,
then J does support asynchronous callbacks for these events, and in that
callback you could do the update as usual.
But in J we tend to think more in terms of functions (verbs) and compositions
(conjunctions), so that for example you wouldn't have
a data (noun) relationship like this:
AVERAGE_SIZE =: (+/ % #) SIZES NB. AVERAGE_SIZE and SIZES are nouns
you'd be much more likely to express the relationship in terms of verbs and
conjunctions, like this [1]:
avgSize =: (+/ % #)@:sizes NB. avgSize and sizes are
verbs
-Dan
[1] These two sentences can be "read" the same in English ("the average size
is the average of the sizes"), but renders the value
of avgSize timeless, in a sense. That is, since the value of (the verb)
"sizes" is always correct, then so is the value of avgSize,
because that is just a simple functional (stateless, side-effect-free) verb on
top of sizes.
Sorry if that's unclear; it's a hard concept to express. I once saw a
presentation in an APL conference in Florida where a
presenter hit this on the head, but I've forgotten how he expressed it.
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