Comma Bar
Monadic Comma Bar means

Table

      ⍪ 2 3 4
2
3
4
      cube    ⍝ 3D array
1 2
3 4
   
5 6
7 8
      ⍪ cube
1 2 3 4
5 6 7 8
Dyadic Comma Bar means

Catenate First

      mat
1 2 3
4 5 6

      mat ⍪ 0
1 2 3
4 5 6
0 0 0

      mat ⍪ 7 8 9
1 2 3
4 5 6
7 8 9

Language Elements