⍚ — Agenda

Keys: Alt-Minus Backtick

selector⍚cases derives a function that selects a branch on each call. cases is a nonempty vector of functions. An array among them acts as a constant function. The selector can be a unit index or a function returning one. Indices are integral and count from 0, and negative indices count from the end. A Boolean selector picks case 0 for $f and case 1 for $t.

cases←[- ⊢] ⋄ abs←0≤ ⍚ cases ⋄ abs¯3          ⍝ 3
cases←[- ⊢] ⋄ abs←0≤ ⍚ cases ⋄ abs3           ⍝ 3
mul←1⍚[+ ×] ⋄ 2 mul 3                         ⍝ 6
mul←¯1⍚[+ ×] ⋄ 2 mul 3                        ⍝ 6
choose←>⍚[- ÷] ⋄ 12 choose 3                  ⍝ 4
nonneg←0≤ ⍚ [0 ⊢] ⋄ nonneg¨ ¯3 4               ⍝ 0 4

A function selector runs once with the original arguments. Only the selected branch runs, with those same arguments. Index arrays do not map over branches or construct trains.

Errors

  • RANK: an index that is not a unit
  • INDEX: out-of-range index
  • DOMAIN: nonnumeric or nonintegral index