Index Origin (⎕IO)

⎕IO controls whether indexing starts at 0 or 1. MARPLE defaults to ⎕IO←1.

Setting index origin

      ⎕IO←1
      ⍳5
1 2 3 4 5
      ⎕IO←0
      ⍳5
0 1 2 3 4

Affected functions

⎕IO affects all index-producing and index-consuming operations:

Function	Effect
⍳ (iota)	Generated indices start at ⎕IO
⌷ (from)	Index values interpreted relative to ⎕IO
V[i] (bracket indexing)	Index values interpreted relative to ⎕IO
⍋ (grade up)	Returned indices start at ⎕IO
⍒ (grade down)	Returned indices start at ⎕IO
⍳ (index-of, dyadic)	Returned indices start at ⎕IO; not-found value is (≢⍺)+⎕IO

Permitted values

Only 0 and 1 are meaningful values for ⎕IO.