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 <[email protected]
<mailto:[email protected]>> 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 [email protected]
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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