The Constant () operator

Dyalog 17.1 defines with a function operand ("Commute").

Dyalog 18.0 will allow an array operand: A is the function which returns A.

ranks  /(13)/
suits  /(4)/
ranks  //(13)
suits  //(4)

The derived function A behaves identically to A{⍺⍺}, or the train (A⊣⊢). But it's different from {A}, which looks up the name A when run.

attrs    ¨ (¨13 4)
attrs  (↓⍉) (/)¨ 13 4