I wrote:
> zUr3=: (2$:1 0,~1+]) : ([EMAIL PROTECTED](>:@[$:],1,0$~1={)@.(<:{.))
Arie Groeneveld responded:
> I want to avoid the `
A knotty problem. Let's see if I can untie it:
NB. Look ma, no ` !
zUr4=: (2$:1 0,~1+]) : ([EMAIL PROTECTED] :. (>:@[$:],1,0$~1={)^:(_1
^(<:{.)))
zUr4 7
1 0 1 1 0 1 0 1 1 0 1 1 0
(zUr -: zUr4) 100
1
I know. Cheap shot. But you did say:
> I just want to come up with a wide variation on the subject
Onward then. Studying further, I better understand what your verb is doing.
Another way to avoid the ` is by keeping ALL your control data in the LHA.
That is, you can "include the behead" by obviating the need for it:
zUr5 =: (1 0 $:~ 1 , >:) : (((1 0 + [) $: ] , 1 , 0 #~ 1= ({~
{.)~)^:(</@[))
zUr5 7
1 0 1 1 0 1 0 1 1 0 1 1 0
(zUr -: zUr4) 100
1
But that's still not what you _really_ want:
> is there a way to do this iteration by not dragging
> along the iterator.
The previous verbs are recursive; if you want an interative formulation, you
need to drop the $: . That is, the "purely iterative" format would use
only ^: .
If we could somehow calculate the current index from the argument, it would
permit the form:
(, 1 , 0 #~ 1 = ({~ calcIdx))^:n
which is much cleaner.
At first glance the verb calcIdx is unobtainable, as the stepwise index
is lost; the argument grows as a function of its previous states (i.e. it is
a recurrence relation), so we cannot use the length of the argument. But
then, it occured to me that one and only one 1 , is added at every step.
So the definition of calcIdx is simply +/ . Therefore we obtain:
zUr6 =: $:&1 0 : ((, 1 , 0 #~ 1 = ({~ +/))@:]^:[)
zur6 7
1 0 1 1 0 1 0 1 1 0 1 1 0
(zUr -: zUr6) 100
1
Now, I personally find forms like u@:]^:[ unappealing. Usually I try to
convert them into the equivalent x u&n y form. This is especially true
when I also see a bound argument. In this case, the argument isn't bound,
but it is defaulted. And losing the monad would also clean up the
parenthesis mess a bit. But I leave the reforumlation as an exercise for
the reader.
I hope this helped.
G-Dan
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