[Jprogramming] Three Simple Questions

[Henry Rich]

To split hairs, an empty array does have a type.  That type determines 
what is produced if you apply {. for example.  But many verbs, including 
x -: y, ignore the type of an empty array. Importantly, most verbs treat 
an empty array of boxes as if it were not boxed.

Henry Rich

On 12/2/2017 10:36 AM, Murray Eisenberg wrote:
> To test whether a noun is a string, there’s the translation into J of one of the first APL idioms I ever learned:
>
>            stringQ =: ‘' -: 0 $ [
>
> Unfortunately, that does not work in J, because a J empty array does not seem to have what in APL was called a “type”; in particular, in J (and similarly in some versions of APL):
>
>          ‘'  -: i. 0
>     1
>      
> Hence the need in J for the workaround that Raul shows, namely, doing a 1{. instead of a 0$.
>
>> On1 Dec 2017 21:34:33 -0500,Raul Miller <rauldmiller at gmail.com <mailto:rauldmiller at gmail.com>> wrote:
>>
>>
>> 1. What do you mean by "an object is string"?
>>
>> This might do it:
>>    isString=: ' '= 1{.0{.,
>>
>> But note that this approach ignores the number of dimensions of the
>> value (and don't get me started on "objects").
> ——
> Murray Eisenberg                                murray at math.umass.edu
> Mathematics & Statistics Dept.
> Lederle Graduate Research Tower      phone 240 246-7240 (H)
> University of Massachusetts
> 710 North Pleasant Street
> Amherst, MA 01003-9305
>
>
>
>
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