Hi,

Not a general answer about gerunds or tacit conditionals, but a particular 
solution for seq:

   seq=: [ + (* * i.@>:@|)@-~
   3 seq 7
3 4 5 6 7
   3 seq~ 7
7 6 5 4 3

Cheers,
Louis

> On 6 Apr 2018, at 22:23, Devon McCormick <devon...@gmail.com> wrote:
> 
> Hi -
> 
> I'm working with selecting sequential items from a vector given a starting
> and an ending point as a pair of integers.  If we assume we always get the
> pair as (lesser, greater), something like this suffices:
> 
>   seq=: {. + [: i. [: >: -~/
>   seq 3 7
> 3 4 5 6 7
> 
> However, if our assumption about the order of our points is violated, we
> get nonsense:
> 
>   seq 7 3
> 7 8 9
> 
> Just for robustness, how could we write a version of "seq" that would
> return the sequence in reverse order in this latter case, i.e. give the
> proper sequence from seven to three: 7 6 5 4 3 ?
> 
> I generalized the "seq" verb to remove the ordering assumption: my idea was
> to generate the ascending sequence, then flip it if >/y is true.  I tried
> this with "agenda" but am not sure how to get it to work on one thing - the
> ascending vector - on the basis of comparison of another thing - the pair
> of integers.
> 
> I did achieve this using the "power" conjunction:
> 
>   seq=: 3 : '|.^:(>/y)](<./ + [: i. [: >: >./ - <./) y'
>   seq 3 7
> 3 4 5 6 7
>   seq 7 3
> 7 6 5 4 3
> 
> Does anyone have any ideas for a more elegant, preferably tacit, solution?
> 
> Thanks,
> 
> Devon
> -- 
> 
> Devon McCormick, CFA
> 
> Quantitative Consultant
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