Indexing

Z←R[L], R[L]←A, and R[L]f←A are all extended to allow both Reach and Scatter indexing.

L is a nested array of integer scalars and/or vectors, suitable for indexing R.

R is an arbitrary array.

A is an arbitrary array.

Reach Indexing: If L⊃R is valid, it is equivalent to ⊃R[⊂L]

Scatter Indexing: If L⌷R is valid, it is equivalent to R[⊃∘.,/L]

Both Reach and Scatter indexing may appear together within a single instance of R[L], R[L]←A, and R[L]f←A

For example, in origin-1

      V←'123'(⊂4 5)
      V[1 (2 ⍬ 1)]
 123 4

Z←R[L], R[L]←A, R[L]f←A, L⌷R, and L⊃R are all extended to allow negative index values.

L is a nested array of integer scalars and/or vectors, suitable for indexing R.

That is, if the largest allowed index value is N, then the previous allowable range of values was ⎕IO to N, inclusive. Now, the allowable range of values is 1 ¯1[1]-N to N, inclusive. For example, A, A[⍳⍴A], and A[⍳-⍴A] are all identical for any array A in either origin.

R is an arbitrary array.

A is an arbitrary array.

For example, in origin-1

      V←'123'(⊂4 5)
      V[¯1 (0 ⍬ 1)]
 123 4