In retrospect, I probably should not have used #. and instead done
something like this:
select. *nc;:'u v'
case. 0 0 do. assert. 0 NB. invalid
case. 0 1 do. m v y NB. left bond
case. 1 0 do. y u n NB. right bond
case. 1 1 do. ([: u v)"v y NB. compose monad
Or perhaps I should have used the raw nc values directly?
As for nc itself, vsapl had a primitive quadNC where quad was a single
character which looks like a box (very like the character chrome and
IE use for unicode when font support is missing). I think that J
includes built-in covers for cases like that. Many foreigns do not
have predefined cover names.
There's some interesting bits of history here relating to the old "i
beam" and "quad", but that probably belongs in another thread.
--
Raul
On Wed, Oct 24, 2012 at 9:09 PM, Peter B. Kessler
<peter.b.kess...@oracle.com> wrote:
> Spectacular!
>
> I was curious what "nc" was, because *I* don't remember defining that verb.
> I discovered
>
> nc
> 4!:0
>
> That is, nc is "pre-defined" as a name for 4!:0. 4!:0 is the foreign
> function verb that returns the "class" of a boxed name as an integer.[1] Is
> there a list of pre-defined names for the foreign functions? (Or do I just
> have to read the source? :-)
>
> Raul Miller's selector is about boxing the argument names with Words (;:),
> classifying the argument names (with 4!:0, nc), differentiating nouns (class
> 0) from verbs (class 3) with signum (*), and then using BaseTwo (#.) to
> distinguish what the pair of arguments are. The selector is worth studying
> in itself, but the model of & is clarity itself.
>
> ... peter
>
> [1] http://www.jsoftware.com/help/dictionary/dx004.htm
>
>
> Raul Miller wrote:
>>
>> On Wed, Oct 24, 2012 at 3:27 AM, Linda Alvord <lindaalv...@verizon.net>
>> wrote:
>>>
>>> m&v y ↔ m v y This is the definition of bond (monadic)
>>>
>>> u&v y ↔ u v y . This is the definition of compose (dyadic)
>>>
>>>
>>> =&{: is the definition which I used earlier as =&{: B
>>>
>>> I was told that I was using & dyadically so it was compose.
>>
>>
>> We need to be careful about using the word "it" in learning contexts.
>> Also, J grammar is regular, so we need to be very careful when
>> describing the use of that grammar.
>>
>> In J, "dyad" refers to the combining definition (usually of a verb,
>> since verbs have two definitions), while "monad" refers to the
>> non-combining definition (usually of a verb...)
>>
>> Anyways, I'm having a problem with "I was told that I was using &
>> dyadically so it was compose." because & in =&{: is compose but not
>> because & was being used dyadically.
>>
>> The & itself is used dyadically in =&{: and in 1&+ and in *&2 but only
>> one of those is compose. And all three of those derived verbs have
>> both monadic and dyadic definitions. Instead "compose" would be
>> because both arguments to & were verbs. (Which was probably the
>> intent of the "it was compose" sentence, but the words were wrong for
>> me.)
>>
>> It might be interesting to write a J conjunction which acts like &
>>
>> ampersand=:2 :0
>> NB. monad
>> select. #.*nc;:'u v'
>> case. 0 do. assert. 0 NB. invalid
>> case. 1 do. m v y NB. left bond
>> case. 2 do. y u n NB. right bond
>> case. 3 do. ([: u v)"v y NB. compose monad
>> end.
>> :
>> NB. dyad (combining form)
>> select. #.*nc;:'u v'
>> case. 0 do. assert. 0 NB. invalid
>> case. 1 do. (m ampersand v)^:x y NB. left bond
>> case. 2 do. (u ampersand n)^:x y NB. right bond
>> case. 3 do. x (([: v [) u ([: v ]))"v y NB. compose dyad
>> end.
>> )
>>
>> Note that I would need to introduce another level of abstraction if I
>> wanted an immediate syntactic warning for the invalid case.
>>
>> amp=:2 :0
>> select. #.*nc;:'u v'
>> case. 0 do. assert. 0 NB. invalid
>> case. 1;2;3 do. u ampersand v
>> end.
>> )
>>
>> Note also that this implementation displays differently from the
>> builtin (for the cases where the resulting derived verb is not used to
>> generate a result). But unless I have made an error these will
>> function the same way the built in works.
>>
>> I hope this helps,
>>
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