Oops, yes. Sorry about that.
I should have said:
amend=: (0:{::)`(1:{::)`(2:{::)}~
(I'm working right now from a machine where J doesn't run, and I
forget details when I don't test my code.)
Thanks,
--
Raul
On 7/6/14, Jose Mario Quintana <[email protected]> wrote:
> Raul wrote:
> "
> For example:
> amend=: 0&{::`(1&{::)`(2&{::)}
> amend 0;2 3 5;7#9
> 9 9 0 0 9 0 9
> "
>
> Actually,
>
> JVERSION
> Installer: j602a_win.exe
> Engine: j701/2011-01-10/11:25
> Library: 6.02.023
>
> amend=: 0&{::`(1&{::)`(2&{::)}
> amend 0;2 3 5;7#9
> |rank error: amend
> | amend 0;2 3 5;7#9
> |[-3]
>
> However,
>
> amend=. _: 0&{::@]`(1&{::@])`(2&{::@])} ]
> amend 0;2 3 5;7#9
> 9 9 0 0 9 0 9
>
> I use a slight variation of this verb occasionally; yet, I find the forms
> <@:v N} ] and v N} ] extremelly useful for writing tacitly (and I write
> tacitly all the time).
>
>
>
> On Sun, Jul 6, 2014 at 6:42 AM, Raul Miller <[email protected]> wrote:
>
>> I would agree that amend is seldom useful in much the same way that
>> computers are seldom useful. That is: it depends on what you mean by
>> "seldom" (and, for that matter, "useful").
>>
>> Generally speaking, } is one of the less common characters that I use
>> when I write in J, but I do use it.
>>
>> Also, in addition to the very fine 0:`[`]} which behaves something like
>> this:
>>
>> 2 3 5 0:`[`]} 7#9
>> 9 9 0 0 9 0 9
>>
>> (Aside: note that in the above expression 2 3 5 is a word, and 0: is a
>> separate word. Try ;:'2 3 5 0:`[`]} 7#9' if you want proof.)
>>
>> ... in addition to that approach, you can also arrange so that all
>> arguments are given in an argument list, if you use
>> 0&{::`(1&{::)`(2&{::)}
>>
>> For example:
>> amend=: 0&{::`(1&{::)`(2&{::)}
>> amend 0;2 3 5;7#9
>> 9 9 0 0 9 0 9
>>
>> But, as with everything, whether this is a good thing or not depends
>> on what you are trying to do...
>>
>> Which leads back to the question: what are you trying to do?
>>
>> Thanks,
>>
>> --
>> Raul
>>
>> On 7/6/14, Ric Sherlock <[email protected]> wrote:
>> > I don't agree that Amend is seldom useful. I do agree that it isn't the
>> > easiest thing to get your head around (perhaps why you have found other
>> > ways to getting stuff done).
>> >
>> > Aai has shown how to tacitly use Amend so it seems that 13 : is not
>> > smart
>> > enough to give you a tacit equivalent. I suspect the reason Amend has
>> been
>> > defined as an adverb is that it requires 3 arguments: the array to
>> > amend,
>> > the indicies to amend, the replacement data. Compare that to From which
>> > only requires 2 bits of info (the array, the indicies).
>> >
>> >
>> >
>> > On Sun, Jul 6, 2014 at 7:53 PM, Ian Clark <[email protected]> wrote:
>> >
>> >> I think Erling is quite right, if you take what he says literally:
>> "Amend
>> >> is seldom useful for indexed replacement when you write tacit J".
>> >>
>> >> I'd go further and say "Amend is seldom useful." Period. I write a lot
>> of
>> >> J
>> >> code and I hardly ever use it.
>> >>
>> >> To someone coming from C (say), this cries out for explanation. In C,
>> just
>> >> about everything is done by keyhole surgery, i.e. by tinkering with
>> >> whatever happens to be at the end of a pointer (read: index). In J,
>> >> just
>> >> about nothing is done that way.
>> >>
>> >> Let me give an example. Suppose I want to write a verb to zero the x'th
>> >> element of a list y ...
>> >> I can easily write it as an explicit verb:
>> >>
>> >> zero=: 4 : '0 x} y'
>> >> 3 zero i.6
>> >> 0 1 2 0 4 5
>> >>
>> >> But "13 :" refuses to give me an equivalent tacit verb ...
>> >>
>> >> 13 : '0 x}y'
>> >> 4 : '0 x}y'
>> >>
>> >> Is this just a shortcoming of "13 :" ? Does anyone know a "nice" tacit
>> >> equivalent? I don't.
>> >>
>> >> Contrast this with what happens if I switch round 0 and x (...which
>> gives
>> >> me a verb to replace the first element of a list y with x). In this
>> >> case
>> >> "13 :" does deliver me a nice simple tacit equivalent ...
>> >>
>> >> 13 : 'x 0}y'
>> >> 0}
>> >>
>> >> So why doesn't 13 : '0 x}y' do something equally as nice? It's all
>> >> explained in http://www.jsoftware.com/jwiki/Vocabulary/curlyrt#dyadic .
>> >> But
>> >> that doesn't really explain to a newcomer why Amend was designed as an
>> >> adverb:
>> >> x m} y
>> >> with (index) m as an *operand*, not an *argument*.
>> >>
>> >> Yes, I can write a tacit verb to zero the x'th element of list y ...
>> >>
>> >> zero2=: 13 : 'y * y~:x'
>> >> 3 zero2 i.6
>> >> 0 1 2 0 4 5
>> >> zero2
>> >> ] * ~:
>> >>
>> >> ... but not by using Amend, which is quite simply not useful in that
>> role.
>> >> Though I'm not claiming it can't be done - in fact there's a worked
>> >> example
>> >> in: http://www.jsoftware.com/jwiki/Vocabulary/curlyrt#dyadic under
>> "More
>> >> Information". But I wouldn't call it "nice".
>> >>
>> >> This illustrates the J approach to programming:
>> >> http://www.jsoftware.com/jwiki/Vocabulary/Loopless -and how it
>> contrasts
>> >> with the C approach. Henry would explain it far better than I can, but
>> >> he's
>> >> busy.
>> >>
>> >> IanClark
>> >>
>> >>
>> >> On Sat, Jul 5, 2014 at 8:59 PM, Erling Hellenäs <
>> [email protected]>
>> >> wrote:
>> >>
>> >> > Hi all !
>> >> >
>> >> > When you write tacit code, the index m used by Amend, syntax
>> description
>> >> > x m} y, is a constant?
>> >> > Normally you have a variable you want to use for indexing? This means
>> >> > Amend is seldom useful for indexed replacement when you write tacit
>> >> > J?
>> >> > Are there any descriptions of nice ways to do indexed replacement in
>> >> tacit
>> >> > J?
>> >> > As with Amend, the result has to be a new variable, of course.
>> >> >
>> >> > Cheers,
>> >> >
>> >> > Erling Hellenäs
>> >> >
>> >> > ----------------------------------------------------------------------
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>> >> >
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>>
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