Index Origin ⎕IO

⎕IO determines the index of the first element of a non-empty vector.

⎕IO is an implicit argument of:

• monadic functions: ⍳, ?, ⍒, ⍋, ⍸
• dyadic functions: ⍳, ?, ⍒, ⍋, ⍉, ⊃, ⌷, ⍸
• operators: ⌸, @
• system functions: ⎕FX, ⎕DMX
• other syntax: bracket indexing and bracket axis, indexed assignment

⎕IO may be assigned the value 0 or 1. The value in a clear workspace is 1. ⎕IO has Namespace scope.

Examples

        ⎕IO←1
        ⍳5
1 2 3 4 5

        ⎕IO←0
        ⍳5
0 1 2 3 4

        +/[0]2 3⍴⍳6
3 5 7

        'ABC',[¯.5]'='
ABC
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