when-empty ( ... seq quot: ( ... -- ... obj ) -- ... seq/obj )
Factor handbook » The language » Collections » Sequence operations » Control flow with sequences

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Vocabulary
sequences

Inputs

seq	a sequence
quot	the first quotation of an if-empty

Outputs

seq/obj

an object

Word description
Makes an implicit check if the sequence is empty. An empty sequence is dropped and the quot is called.

Examples
This word is equivalent to if-empty with an empty second quotation:

USING: sequences prettyprint ; { } [ { 4 5 6 } ] [ ] if-empty .
{ 4 5 6 }

USING: sequences prettyprint ; { } [ { 4 5 6 } ] when-empty .
{ 4 5 6 }

Definition

IN: sequences

: when-empty
    ( ... seq quot: ( ... -- ... obj ) -- ... seq/obj )
    [ ] if-empty ; inline