[Jprogramming] argument for under

[Brian Schott]

The following expression accomplishes my goal when the array on the right
(i. 5 4 3 here) needs to be rotated by 1, the leftmost 1. But I want that 1
to be an argument, also.

;/(1|."_1]) &. (1 0 2&|:)i.5 4 3

​But my attempts such as the following, produce errors.
Can you suggest a solution, preferably tacit?

   ;/1(([|."_1]) &. (1 0 2|:]))i.5 4 3
|index error
|   ;/1    (([|."_1])&.(1 0 2|:]))i.5 4 3
​
​Thanks,​


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(B=)