I'm not sure this issue completely matches my difficulty with ^:1 0 1 because
that was fixed with ^:[
to be clear:
(0 0;1 1;2 2){ i.3 3
0 4 8
(0 0;1 1;2 2) (+:@:])`[`]}i.3 3
|rank error
1 1 1 (0 0;1 1;2 2)}i.3 3
1 1 2
3 1 5
6 7 1
The problem is actually with v0 and not v1... described/fixed below. I agree
that it is not a bug though:
To expand on the questionable design decisions:
There is no good reason for item amend to be an adverb.
The problem with the gerund version of amend that Henry helped with is in v0.
It produces x v0 y and not x ([ v0 v1) y which would seem infinitely more
useful. The v2 part seems unnecessary.
At any rate though:
(0 0;1 1;2 2) (+:@:{)`[`]}i.3 3
0 1 2
3 8 5
6 7 16
+: amend (0 0;1 1;2 2) i. 3 3
0 1 2
3 8 5
6 7 16
(0 0;1 1;2 2) (3 + {)`[`]}i.3 3
3 1 2
3 7 5
6 7 11
----- Original Message -----
From: Dan Bron <[email protected]>
To: "[email protected]" <[email protected]>
Cc:
Sent: Sunday, March 30, 2014 1:34:27 PM
Subject: Re: [Jprogramming] Item amend ~: index error.
I recommend cultivating a skepticism of the thought "this is a bug in J". It's
a thought-stopping reaction, and almost always wrong.
That's not to say J has no bugs: no, I mean "almost always" in the
measure-theoretical sense; while I've found plenty of bugs in J, their number
is absolutely dominated by the number of bugs I've found in my understanding of
J. So now my first reaction is to debug my mental model before I try to debug J.
Here's how I might approach that in your current case. First, I recognize that
the argument to }, here, is a 3-element gerund, and the derived verb being
invoked dyadically:
> 3 +`((0 0;1 1;2 2)"1)`]} i.3 3
So I look up that case in the definition of } :
x (v0`v1`v2)} y ↔️ (x v0 y) (x v1 y)} (x v2 y)
Next, I would test this assertion the DoJ is making, against my current example:
x =: 3
y=:i.3 3
v0=:+
v1=:(0 0;1 1;2 2)"1
v2=:]
m=: v0`v1`v2
benchmark=:x m} y
test =:(x v0 y) (x v1 y)} (x v2 y)
test-:benchmark
1
So, since the results agree with each other, and therefore the Dictionary,
there is no bug in J (at least not here). Which means, if I disagree with
either result or the fact that they are identical, the bug must be in my mental
model.
Make sense?
-Dan
PS: I think I know what's confusing you, and it's related to your earlier
frustration with ^:(1 0 1"_) .
I have a half-written draft in response to that, but to treat it properly and
clearly would take more time than I anticipated, so I didn't send it.
The short story is that conjunctions and adverbs, for all their power, have on
critical handicap with respect to verbs: they can't slice or dice their
arguments. Conjunctions and adverbs always address arguments in toto; there is
no (straightforward) way for them to operate piecewise. When you ask an
operator to work piecewise, typically you'll just end up making multiple copies
of the entire argument (as happens with ^:1 0 1).
That's why we often say that the verb has primacy in J: most code is written as
verbs and most tools assist in writing verbs. In fact, this is what adverbs and
conjunctions are mostly intended to do: help write verbs, rather than stand by
themselves (in the ideal J statement, you wouldn't even see the advs/conjs;
they would fade into the background, so we could focus on the logic expressed
by the verbs. Which is why we find trains so elegant and bicker about a better
use for "hook", how and whether to interpret juxtaposed nouns, etc).
The shining example here is: " . It is absolutely the most used conjunction in
J (if you count implicit uses) and is designed precisely to let J verbs operate
piecewise, in a straightforward, non-intrusive (often literally invisible) way.
To let adverbs and conjunctions and adverbs operate piecewise (in a
straightforward way), we'd need some kind of meta-" that could take operators
as arguments, but currently no wordclass in J has higher precedence (binding
power) than adverbs and conjunctions, so that's not possible.
> On Mar 30, 2014, at 1:35 PM, Pascal Jasmin <[email protected]> wrote:
>
> I'm sure your explanation is helpful to many, but the reason for my comment
> comes from the natural frustrations of "I wish the computer would do what I
> meant instead of what I say" moments and then the obvious consequence of
> obviously "I don't always understand what I say.", which even if we all
> acknowledge to be true, is not the foremost thought when
> debugging/troubleshooting.
>
> ~ is the demon that will haunt beginners the most. Passive is by far the
> most common use of ~, and the most intuitively understandable (though all 3
> are fairly quite straightforward), but its conceptually linked most directly
> to Passive.
>
> I do not like or recommend the practice of replacing J primitives with words
> such as 'verb define' because it obfuscates the parsing understanding needed
> to read and write J. However, in the case of ~, (though I don't do it), it
> would have saved me many headaches if I had defined 3 adverbs and used them.
>
> For interest what is said with: (i. 3 3) }~ (0 1 2) is:
>
> 0 1 2 (i. 3 3) } 0 1 2
>
>
> On another note, } is overly complicated, and IMO poorly designed, though
> Eelvex's example is something I just learned today towards explaining it.
>
>
> (0 1 2) } (i. 3 3)
> 0 4 8
>
>
> the above is incredibly cool, as it retrieves the diagonal from i. 3 3. But
> note, the unfortunate asymetry with { which would have made a more
> approachable design decision:
>
> (0 1 2) { (i. 3 3)
> 0 1 2
> 3 4 5
> 6 7 8
>
>
> so, this happens:
> 1 (0 1 2) } (i. 3 3)
> 1 1 1
> 1 1 1
> 1 1 1
>
> +: (0 1 2) } (i. 3 3)
> 0 8 16
>
> (0 1 ) } (i. 3 3)
> |length error
> | (0 1)}(i.3 3)
>
> (0 1 ) { (i. 3 3)
> 0 1 2
> 3 4 5
>
>
> The key to understanding }'s behaviour is that m} has both a monadic and
> dyadic verb result. Which is completely unobvious for something called
> amend. (An intuitive imagination based understanding (as opposed to RTFM
> based understanding which separates item amend from amend definitions) would
> be that n} returns an adverb instead of a verb, which can then take u or m to
> update y.
>
> I recommend using the following conjunction most of the time:
>
> amend_z_ =: 2 : 0 NB. v is n or n{"num
> s=. v"_ y
> (u"_ (s{y)) (s}) y
> :
> s=. v"_ y
> (x u"_ (s{y)) (s}) y
> )
>
>
> Though it loses the quirky feature of obtaining the diagonal (Item Amend), it
> gaI'm sure your explanation is helpful to many, but the reason for my comment
> comes from the natural frustrations of "I wish the computer would do what I
> meant instead of what I say" moments and then the obvious consequence of
> obviously "I don't always understand what I say.", which even if we all
> acknowledge to be true, is not the foremost thought when
> debugging/troubleshooting.
>
> ~ is the demon that will haunt beginners the most. Passive is by far the
> most common use of ~, and the most intuitively understandable (though all 3
> are fairly quite straightforward), but its conceptually linked most directly
> to Passive.
>
> I do not like or recommend the practice of replacing J primitives with words
> such as 'verb define' because it obfuscates the parsing understanding needed
> to read and write J. However, in the case of ~, (though I don't do it), it
> would have saved me many headaches if I had defined 3 adverbs and used them.
>
> For interest what is said with: (i. 3 3) }~ (0 1 2) is:
>
> 0 1 2 (i. 3 3) } 0 1 2
>
>
> On another note, } is overly complicated, and IMO poorly designed, though
> Eelvex's example is something I just learned today towards explaining it.
>
>
> (0 1 2) } (i. 3 3)
> 0 4 8
>
>
> the above is incredibly cool, as it retrieves the diagonal from i. 3 3. But
> note, the unfortunate asymetry with { which would have made a more
> approachable design decision:
>
> (0 1 2) { (i. 3 3)
> 0 1 2
> 3 4 5
> 6 7 8
>
>
> so, this happens:
> 1 (0 1 2) } (i. 3 3)
> 1 1 1
> 1 1 1
> 1 1 1
>
> +: (0 1 2) } (i. 3 3)
> 0 8 16
>
> (0 1 ) } (i. 3 3)
> |length error
> | (0 1)}(i.3 3)
>
> (0 1 ) { (i. 3 3)
> 0 1 2
> 3 4 5
>
>
> The key to understanding }'s behaviour is that m} has both a monadic and
> dyadic verb result. Which is completely unobvious for something called
> amend. (An intuitive imagination based understanding (as opposed to RTFM
> based understanding which separates item amend from amend definitions) would
> be that n} returns an adverb instead of a verb, which can then take u or m to
> update y.
>
> I recommend using the following conjunction most of the time:
>
> amend_z_ =: 2 : 0 NB. v is n or n{"num
> s=. v"_ y
> (u"_ (s{y)) (s}) y
> :
> s=. v"_ y
> (x u"_ (s{y)) (s}) y
> )
>
>
> Though it loses the quirky feature of obtaining the diagonal (Item Amend), it
> gains the feature of updating y in an intuitive (symetrical to {) way that
> accepts a verb for the updating.
>
> +: amend ( 1 2) i. 3 3
> 0 1 2
> 6 8 10
> 12 14 16
>
>
> 3 + amend 1 +: amend ( 1 2) i. 3 3
> 0 1 2
> 9 11 13
> 12 14 16
>
>
>
> the gerund } is weird too. Here is a result I don't understand (might be a
> bug?):
>
> 3 +`((0 0;1 1;2 2)"1)`]} i.3 3
> 9 1 2
> 3 10 5
> 6 7 11
>
>
>
> ----- Original Message -----
> From: Dan Bron <[email protected]>
> To: "[email protected]" <[email protected]>
> Cc:
> Sent: Sunday, March 30, 2014 9:16:51 AM
> Subject: Re: [Jprogramming] Item amend ~: index error.
>
> You can tell immediately whether ~ is performing passive, reflexive , or
> evoke.
>
> Did you pass it a noun? Then it's evoke (this is very rare and very obvious:
> remember, as an adverb, ~'s argument is fixed at runtime, so you'd literally
> have to write or see a noun directly to the left of ~).
>
> You didn't pass it a noun? Ok, by definition, you passed it a verb. So ~
> consumed that verb and produced a new verb. Did you pass that new verb one
> argument, or two arguments?
>
> If you passed the new verb one argument (aka "invoked the monad") then ~ will
> act in its reflexive capacity. If you passed the new verb two arguments (aka
> "invoked the monad") then ~ will act in its passive capacity.
>
> In other words, f~ ↔️ (] f ]) : (] f [) . That is, given a verb f, f~ will
> produce an ambivalent verb which will always invoke the dyadic valence of f
> (the monadic valence of f is thus ignored and therefore irrelevant). When f~
> is invoked, the left argument to f will always be the right argument of f~ .
>
> Thus, the only difference between passive and reflexive is the right argument
> to f, which will be the left argument of f~ if it has one (ie if f~ was
> invoked dyadically) or the same old right argument as before if it doesn't
> (ie if f~ was invoked monadically and the only argument around to use is on
> the right).
>
> So ~ is hardly a demon from hell, because you know what you're getting when
> you invoke it. The incantations are simple and the consequences predictable.
>
> -Dan
>
> Ok, need a mnemonic?
>
> 'name'~ : evoke the name (call upon, summon up, conjure, recall)
>
> verb~ y : reflect the argument (mirror, create a perfect image, clone, put a
> mirror up so the verb sees two identical copies, etc)
>
> x verb~ y : use the passive voice (switch the subject and object, invert the
> sentence, etc):
>
> Pascal invoked Astaroth
> Astaroth was invoked by Pascal
>
> [do not try this at home]
>
> [1] "Why was ~ on a dyadic verb named "passive"?
> http://www.jsoftware.com/pipermail/general/2007-May/030070.html
>
>
> Sent from my iPhone
>> On Mar 30, 2014, at 8:31 AM, Pascal Jasmin <[email protected]> wrote:
>>
>> } is an adverb.
>> ~ is a demon from hell for errors in that it can do one of 3 things
>> (passive, reflex, evoke), and often its one of the other 2 than you
>> intended. (here you were assuming it would do passive). I'm not 100%
>> positive which of the other 2 it actually gets parsed at here.
>>
>>
>> ----- Original Message -----
>> From: EelVex <[email protected]>
>> To: Programming forum <[email protected]>
>> Cc:
>> Sent: Sunday, March 30, 2014 7:07:05 AM
>> Subject: [Jprogramming] Item amend ~: index error.
>>
>> (0 1 2) } (i. 3 3)
>> 0 4 8
>>
>> (i. 3 3) }~ (0 1 2)
>> |index error
>> | (i.3 3)}~(0 1 2)
>>
>> Why? What's the use of }~ when not used as 'amend'?
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