[Jprogramming] Am I understanding m/y ?

[Martin Kreuzer]

Pattern "left join"---same frame of mind as when 
we staple a couple of pages together (in the 
upper left hand corner, as we usually do).
-M

At 2016-06-14 03:07, you wrote:
>Perhaps easier to see with more 
>formal/expressive verbs:    in =. 1 :'[,'' 
>'',u,'' '',]' NB. String to infix 
>function    ('f0'in)`('f1'in)`('f2'in)/ 'abcde' 
>a f0 b f1 c f2 d f0 e The verbs in the gerund 
>are arranged from left to right starting at the 
>beginning of the array, while application (as in 
>the non-gerund case) proceeds from right to 
>left. I would avoid calling either of these 
>things "unrolling" without further explanation 
>as it's not clear which that would mean. Dan's 
>example has typos, and his wording is vague 
>enough that I can't tell whether it is correct. 
>Marshall On Tue, Jun 14, 2016 at 02:21:37AM 
>+0000, 'Pascal Jasmin' via Programming wrote: > 
>+`-/ 1 2 3 > 0 > +`+`-/ 1 2 3 > 6 > > > I call 
>this as being inserted between items on a right 
>to left basis. > > 1 + 2 - 3 + 4 > > +`-/ 1 2 3 
>4 > _4 > +`-/ 1 2 > 3 > > > > ----- Original 
>Message ----- > From: Dan Bron <j at bron.us> > To: 
>J Programming <programming at jsoftware.com> > 
>Sent: Monday, June 13, 2016 9:04 PM > Subject: 
>Re: [Jprogramming] Am I understanding m/y ? > > 
>Louis wrote: > > > There was some talk a while 
>ago about the ambiguity of the dictionary about 
>the direction of gerund insertion. Reading 
>through the first pages of Iverson's Concrete 
>Math Companion, I stumbled on a snippet of J 
>that dates back to 2002 and was written by 
>Iverson at the bottom of page 6: > > > > 
>http://www.jsoftware.com/books/pdf/cmc.pdf 
><http://www.jsoftware.com/books/pdf/cmc.pdf> > >  
> > > According to this source, gerunds do indeed 
>"unroll" from left to right correctly in the 
>current implementation. > > > I’m also on 
>mobile, so forgive my terse answer and potential 
>misunderstanding of your question, but 
>yes: > > >         v0`v1`v2`v3/ y > > is 
>indeed: > >         
 (_8{y)  v2 (_7{y) v3 
>(_6{y) v0 (_5{y) v1 (_4{y) v2 (_3{y) v1 (_2{y) 
>v0 _1{y > > That is, the insertion of verbs 
>starts at the rightmost (last) elements of y, 
>but the leftmost (first) elements of the gerund 
>G, where  G/y  . > > The rationale for this is 
>left as an exercise for a less lazy respondent 
>(though the right-to-left nature of insertion in 
>y should be familiar to veteran J’ers). > > 
>-Dan > > > > 
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